Cathode for hydrogen generation, cathode for alkaline water electrolysis, cathode manufacturing method, bipolar electrolytic cell, electrolytic cell for alkaline water electrolysis, and hydrogen production method

Abstract

The purpose of the present invention is to provide a negative electrode which maintains a high energy conversion efficiency for a long period of time without an increase in the overvoltage even in cases where start and stop of hydrogen generation are repeated.　In order to achieve the above-described purpose, the present invention provides a negative electrode for hydrogen generation, the negative electrode having, on the surface of a conductive base material, a catalyst layer that contains at least one substance selected from among Pt, Pt oxide and Pt hydroxide and at least one substance selected from among a lanthanoid, a lanthanoid oxide and a lanthanoid hydroxide, while being characterized in that the molar ratio of the elemental Pt to the elemental lanthanoid (Pt : lanthanoid) in the catalyst layer is 95:5 to 65:35.

Description

[Technical Field]

[0001] The present invention relates to a cathode for hydrogen generation, a cathode for alkaline water electrolysis, a method for manufacturing a cathode, a bipolar electrolytic cell, an electrolytic cell for alkaline water electrolysis, and a method for producing hydrogen. [Background technology]

[0002] In recent years, renewable energy technologies such as wind power generation and solar power generation have been attracting attention in order to solve problems such as global warming caused by greenhouse gases such as carbon dioxide and dwindling fossil fuel reserves.

[0003] Renewable energy output is highly variable because it depends on weather conditions. As a result, it is not always possible to transport the electricity generated by renewable energy to the general power grid, raising concerns about the potential for imbalances in power supply and demand and the instability of the power grid.

[0004] Therefore, research is being conducted into converting electricity generated from renewable energy into a form that can be stored and transported, and using this electricity.Specifically, research is being conducted into generating storable and transportable hydrogen through the electrolysis of water using electricity generated from renewable energy, and using this hydrogen as an energy source or raw material.

[0005] Hydrogen is widely used industrially in oil refining, chemical synthesis, metal refining, etc., and in recent years, the possibility of its use has expanded in hydrogen stations for fuel cell vehicles (FCVs), smart communities, hydrogen power plants, etc. For this reason, there are high expectations for the development of technology to obtain hydrogen, especially from renewable energy sources.

[0006] Methods for electrolyzing water include solid polymer water electrolysis, high-temperature steam electrolysis, and alkaline water electrolysis. However, alkaline water electrolysis is considered to be one of the most promising methods because it has been industrialized for several decades, can be carried out on a large scale, and is inexpensive compared to other water electrolysis devices.

[0007] However, in order to adapt alkaline water electrolysis as a means for storing and transporting energy in the future, it is necessary to enable water electrolysis by efficiently and stably utilizing electric power, which has large output fluctuations as described above, and there is a need to solve various issues with electrolytic cells and devices for alkaline water electrolysis.

[0008] It is well known that adopting a so-called zero-gap structure, in which the gap between the diaphragm and the electrode is substantially eliminated, as the structure of the electrolysis cell is particularly effective for solving the problem of reducing the electrolysis voltage in alkaline water electrolysis and improving the power consumption rate of hydrogen production (see Patent Documents 1 and 2). In the zero-gap structure, the generated gas is quickly released to the side of the electrode opposite the diaphragm through the pores in the electrode, thereby reducing the distance between the electrodes and minimizing the occurrence of gas accumulation near the electrodes, thereby reducing the electrolysis voltage. The zero-gap structure is extremely effective in reducing the electrolysis voltage and is adopted in a variety of electrolysis devices. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent No. 5553605 [Patent Document 2] International Publication No. 2015 / 098058 Summary of the Invention [Problem to be solved by the invention]

[0010] However, the conventional cathodes for alkaline water electrolysis described in Patent Documents 1 and 2 have a problem in that the catalyst layer is depleted or detached, resulting in an increase in overvoltage, due to repeated application of a forward current that promotes the intended electrolytic reaction and a reverse current (reverse current) that occurs after the forward current is stopped. Therefore, it has been difficult to maintain high energy conversion efficiency over the long term when using a variable power source such as renewable energy.

[0011] Therefore, an object of the present invention is to provide a cathode that does not increase overvoltage and maintains high energy conversion efficiency for a long period of time even when hydrogen generation is repeatedly started and stopped. [Means for solving the problem]

[0012] That is, the present invention is as follows. (1) at least one of Pt, Pt oxide, and Pt hydroxide on the surface of a conductive substrate; At least one of a metal, oxide, and hydroxide of a lanthanoid element that is electrochemically stable as a trivalent ion within the potential window of water of pH 7 or more and pH 16 or less; A cathode for hydrogen generation having a catalyst layer containing A cathode for generating hydrogen, characterized in that the molar ratio of Pt element to lanthanoid element (Pt:lanthanoid) in the catalyst layer is 95:5 to 65:35. (2) The cathode according to claim 1, which is a cathode for alkaline water electrolysis. (3) The cathode according to (1) or (2), wherein the catalyst layer contains the same type of element as that contained in the conductive substrate. (4) The cathode according to any one of (1) to (3), wherein the catalytic layer comprises a first layer formed on the surface of the conductive base material and a second layer formed on the first layer, the first layer having different molar ratios of platinum and lanthanoid. (5) The cathode according to (4), wherein the molar ratio of the lanthanoid element in the second layer is greater than the molar ratio of the lanthanoid element in the first layer. (6) The cathode according to (4) or (5), wherein the first layer contains the same element as that contained in the conductive substrate. (7) The cathode according to any one of (1) to (6), characterized in that, when the peak area of ​​X-rays diffracted by the (111) plane of Pt metal in the catalyst layer is IPt, and the peak area of ​​X-rays diffracted by the (200) plane and the (111) plane of PtO is IPtO, the value of [IPt / (IPt+IPtO)] is 0.1 or more. (8) The cathode according to any one of (1) to (7), wherein the lanthanoid element is at least one of Nd, Sm, Gd, Tb, and Dy. (9) The cathode according to (8), wherein the lanthanoid element is Nd. (10) The cathode according to any one of (1) to (9), wherein the conductive substrate contains Ni. (11) The cathode according to (10), wherein the conductive substrate is a plain weave mesh made by weaving fine Ni wires having a diameter of 0.05 mm or more and 1.00 mm or less into a mesh size of 20 mesh or more and 60 mesh or less. (12) The cathode according to (10), wherein the conductive substrate is a Ni foil having a thickness of 100 μm or less. (13) The cathode according to any one of (10) to (12), wherein the catalyst layer contains Pt, Nd, and Ni. (14) The cathode according to (12), wherein the catalyst layer comprises the first layer containing Pt and Nd and the second layer containing Pt and Ni. (15) The amount of the catalyst layer is 4.5 g / m 2 More than 20g / m 2 The cathode according to any one of (1) to (14), characterized in that: (16) The amount of Pt element supported in the catalyst layer is 3.5 g / m 2 More than 15g / m 2 The cathode according to any one of (1) to (15), characterized in that: (17) The cathode according to any one of (1) to (16), wherein the catalyst layer contains a hydrogen storage alloy. (18) The cathode according to (17), wherein the catalyst layer contains Pd. (19) 6kA / m2 After applying a reduction current of 15A / m for 1 hour 2 The cumulative discharge amount until the potential reaches +1.12 V (vs. RHE) is 1500 C / m 2 More than 10000C / m 2 The cathode according to any one of (1) to (18), characterized in that: (20) Electric double layer capacitance is 0.01 F / cm 2 More than 0.15F / cm 2 The cathode according to any one of (1) to (19), characterized in that: (21) A coating step of coating the conductive substrate with a coating liquid containing at least a Pt compound and a lanthanoid compound; a precursor layer forming step of drying the coating liquid to form a precursor layer containing Pt and a lanthanoid on the conductive substrate; a calcination step of heating the precursor layer in a temperature range of 300°C to 800°C to obtain a catalyst layer; A method for producing a cathode according to the present invention, characterized by comprising steps that are repeated in order two or more times. (22) A first coating step of coating the conductive substrate containing Ni with a first coating liquid containing at least a Pt compound and Ni; a first precursor layer forming step of drying the first coating liquid to form a first precursor layer containing Pt and Ni on the conductive base material; a first firing step of heating the first precursor layer in a temperature range of 300°C to 800°C to obtain the first layer; After the first step, which is repeated two or more times in sequence, a second coating step of coating a second coating liquid containing at least a Pt compound and an Nd compound onto the conductive substrate on which the first layer has been formed; a second precursor layer forming step of drying the second coating liquid to form a second precursor layer containing Pt and Nd on the first coating layer; a second firing step of heating the second precursor layer in a temperature range of 300°C to 800°C to obtain a second layer; The method for producing a cathode according to (4), further comprising repeating the second step twice or more in sequence. (23) A first coating step of coating the conductive substrate containing Ni with a first coating liquid containing at least a Pt compound and Ni; a first precursor layer forming step of drying the first coating liquid to form a first precursor layer containing Pt and Ni on the conductive base material; a first firing step of heating the first precursor layer in a temperature range of 300°C to 800°C to obtain the first layer; After the first step, which is repeated two or more times in sequence, a second coating step of coating a second coating liquid containing at least a Pt compound and an Nd compound onto the conductive base material on which the first layer has been formed; a second precursor layer forming step of drying the second coating liquid to form a second precursor layer containing Pt and Nd on the first coating layer; a second firing step of heating the second precursor layer in a temperature range of 300°C to 800°C to obtain a second layer; The method for producing a cathode according to (14), further comprising repeating the second step twice or more in sequence. (24) A bipolar electrolytic cell comprising the cathode according to the present invention. (25) A device comprising the cathode and an anode, 6kA / m 2 After applying an oxidation current of 15A / m for 1 hour 2 The cumulative discharge amount until the potential reaches +0.12 V (vs. RHE) is 6 kA / m 2 After applying a reduction current of 15A / m for 1 hour 2 (25) The bipolar electrolytic cell according to (24), wherein the cumulative discharge amount is greater than the cumulative discharge amount until the potential reaches +1.12 V (vs. RHE) when an oxidation current of (26) 6 kA / m 2 After applying an oxidation current of 15A / m for 1 hour 2 The cumulative discharge amount until the potential reaches +0.12 V (vs. RHE) is 10,000 C / m 2 More than 300000C / m 2 The bipolar electrolytic cell according to (24), characterized in that: (27) The bipolar electrolytic cell according to claim 24, wherein the anode contains Ni. (28) 3 to 200 bipolar electrolytic cells according to the present invention; at least one cathode terminal cell; at least one anode terminal cell; An electrolytic cell for alkaline water electrolysis, comprising: (8) A method for producing hydrogen, comprising electrolyzing alkali-containing water using the alkaline water electrolysis cell according to the present invention to produce hydrogen. (29) A method for producing hydrogen, comprising electrolyzing alkali-containing water using the alkaline water electrolysis cell according to (28) to produce hydrogen. (30) The method for producing hydrogen according to (29), characterized in that water containing alkali is electrolyzed using a variable power supply that involves repeating positive current application and stopping of positive current application to produce hydrogen. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a cathode that does not experience an increase in overvoltage and maintains high energy conversion efficiency for a long period of time even when hydrogen generation is repeatedly started and stopped. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a side view illustrating an example of an entire electrolytic cell for alkaline water electrolysis including a bipolar electrolytic cell according to the present embodiment. [Figure 2] FIG. 2 is a diagram showing a cross section of the interior of an electrolytic cell of an alkaline water electrolysis cell including the bipolar electrolytic cell of the present embodiment, the electrolytic cell being enclosed by a dashed square frame in FIG. 1. [Figure 3] FIG. 1 is a diagram showing an outline of an electrolysis device used in Examples and Comparative Examples. [Figure 4] FIG. 1 is a diagram showing an outline of an electrolytic cell for alkaline water electrolysis used in electrolysis tests. [Figure 5]FIG. 5 is a cross-sectional view of the inside of an electrolysis cell of an alkaline water electrolysis cell used in an electrolysis test, the electrolysis cell being a portion of a dashed-dotted rectangular frame X in FIG. 4. [Figure 6] FIG. 5 is a diagram showing a cross section of the inside of an electrolysis cell of an alkaline water electrolysis cell used in an electrolysis test, the electrolysis cell being a part of a rectangular frame Y enclosed by a two-dot dashed line in FIG. 4. [Figure 7] FIG. 1 is a diagram showing an example of discharge curves of the cathode and anode of an example obtained in an electrolysis test. [Figure 8] FIG. 10 is a diagram showing the results of cyclic voltammetry of the cathode of the example obtained in an electrolysis test. [Figure 9] FIG. 10 is a diagram showing the results of cyclic voltammetry of the cathode of the comparative example obtained in an electrolysis test. [Figure 10] FIG. 10 is a diagram showing a spectrum obtained by X-ray photoelectron spectroscopy measurement of the cathode of the example obtained in an electrolysis test. [Figure 11] FIG. 10 is a diagram showing a spectrum obtained by X-ray photoelectron spectroscopy measurement of the cathode of the comparative example obtained in an electrolysis test. [Figure 12] FIG. 1 is a diagram showing an SEM observation image of a cathode of an example obtained in an electrolysis test. [Figure 13] FIG. 10 is a diagram showing an SEM image of a cathode of a comparative example obtained in an electrolysis test. [Figure 14] FIG. 2 is a diagram showing an X-ray diffraction chart of the cathode of the example. [Figure 15] FIG. 2 is a diagram showing a discharge curve of a cathode, a discharge curve of an anode, and a final potential. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail. It should be noted that the present embodiment is an example for explaining the present invention, and the present invention is not limited to the embodiment. In other words, the present invention can be modified in various ways without departing from the gist of the present invention.

[0016] <Cathode for hydrogen generation, cathode for alkaline water electrolysis> The cathode of this embodiment is a cathode for hydrogen generation and a cathode for alkaline water electrolysis, which has a catalyst layer on the surface of a conductive substrate. In hydrogen production by alkaline water electrolysis, reducing energy consumption, specifically the electrolysis voltage, is a major challenge. Because the electrolysis voltage is highly dependent on the hydrogen generation overpotential at the cathode, the performance of the cathode is important.

[0017] The electrolysis voltage for alkaline water electrolysis is divided into the theoretically required voltage for water electrolysis, the overvoltage for the anodic reaction (oxygen generation), the overvoltage for the cathodic reaction (hydrogen generation), and the voltage due to the distance between the anode and cathode. Here, overvoltage refers to the voltage that must be applied in excess of the theoretical decomposition voltage when a certain current is passed, and its value depends on the current value. In other words, using electrodes with a low overvoltage can reduce the power consumption to produce the same amount of hydrogen.

[0018] Furthermore, the cathode of the present embodiment has improved reverse current durability, which not only enables a low overvoltage to be maintained for a long period of time but also has other advantageous effects, such as being less susceptible to corrosion of the cathode substrate and catalytic layer, detachment of the catalytic layer, dissolution in the electrolyte, and adhesion of inclusions to the diaphragm, even when an unstable current such as that from renewable energy is used.

[0019] In order to achieve a low overvoltage, the cathode must have high electrical conductivity, high hydrogen generation ability, high wettability of the electrode surface with the electrolyte, etc. The cathode of this embodiment can satisfy these requirements by containing a metal element such as Pt.

[0020] In one embodiment, the cathode has a catalyst layer on the surface of a conductive substrate, the catalyst layer containing at least one of Pt, Pt oxide, and Pt hydroxide (hereinafter, these may be collectively referred to as "Pt-based compounds"), and at least one of a lanthanoid metal, oxide, and hydroxide (hereinafter, these may be collectively referred to as "lanthanoid-based compounds") that is electrochemically stable as a trivalent ion within the potential window of water from pH 7 to pH 16. As described above, the inclusion of a Pt-based compound in the catalytic layer can reduce the hydrogen generation overvoltage of the cathode. Furthermore, the inclusion of a compound in the catalytic layer that can increase the electric double layer capacity, which is an indicator of the effective area used for electrolysis on the surface of the cathode, can further reduce the overvoltage. To maintain this effect of increasing the electric double layer capacity over a long period of time, the element must be insoluble in the electrolyte in the electrolytic environment, and therefore is preferably electrochemically stable as a solid. Furthermore, the element is preferably one that does not undergo a valence change due to electrochemical oxidation-reduction even when repeatedly exposed to reduction associated with forward current application and oxidation associated with a reverse current generated by the cessation of forward current application. If a valence change occurs, the crystal morphology will change with each cycle of forward current application and cessation of forward current application. Repeated cycles of this change can cause the catalytic layer to physically collapse, inducing an increase in overvoltage. As a result of thorough research conducted from these perspectives, it was discovered that in order to maintain high energy conversion efficiency over the long term without an increase in overvoltage, even when hydrogen generation is repeatedly started and stopped, it is preferable to include in the catalyst layer a lanthanoid element, which is electrochemically stable as a trivalent ion within the potential window of water (pH 7 or higher and pH 16 or lower). For the electrochemical stability of each element within the potential window of water from pH 7 to pH 16, reference was made to Atlas of Electrochemical Equilibria in Aqueous Solutions (by Marcel Pourbaix, published by the National Association of Corrosion Engineers, 1974). That is, by further containing a lanthanoid-based compound that is electrochemically stable as a trivalent ion within the potential window of water of pH 7 or more and pH 16 or less in addition to the Pt-based compound described above in the catalyst layer, deterioration of the cathode can be suppressed and high energy conversion efficiency can be maintained even when the electrolytic cell is operated under a variable power supply.

[0021] In the cathode of this embodiment, the molar ratio of Pt element to lanthanoid element (Pt:lanthanoid) in the catalyst layer is 95:5 to 65:35, preferably 90:10 to 70:30, and more preferably 85:15 to 73:27. The more lanthanoid compound, the higher the electric double layer capacity, and the more effective it is in reducing hydrogen generation overvoltage and improving reverse current durability. On the other hand, lanthanoid compounds, particularly oxides and hydroxides, have low electrical conductivity, so if there is too much, the electrical conductivity of the catalytic layer is impaired and the overvoltage increases. Therefore, in this embodiment, by setting the molar ratio of Pt element to lanthanoid element in the catalytic layer within the above range, the cathode overvoltage can be maintained even lower, even when the electrolytic cell is operated under a variable power supply, and high energy conversion efficiency can be maintained for a long period of time.

[0022] Furthermore, the catalyst layer preferably contains the same type of element as that contained in the conductive base material, because the improved affinity between the catalyst layer and the conductive base material prevents the catalyst layer from falling off the base material and increases the reverse current durability.

[0023] The catalyst layer may also have a laminated structure including a first layer formed on the surface of the conductive substrate and a second layer formed on the first layer, the first layer having different molar ratios of Pt and lanthanoid.

[0024] In the case of a laminated structure, the catalytic layer preferably comprises a first layer formed on the surface of the conductive substrate and a second layer formed on the first layer, and the molar ratio of the lanthanoid element in the second layer is greater than the molar ratio of the lanthanoid element in the first layer, because adding the lanthanoid element to the second layer closer to the surface of the catalytic layer results in a larger amount of the lanthanoid element contributing to electrolysis than adding the lanthanoid element to the first layer, thereby increasing reverse current durability.

[0025] Furthermore, in the case of a laminated structure, it is preferable that the first layer contains the same type of element as the element contained in the conductive base material, because the affinity between the first layer and the conductive base material is improved, which suppresses the catalyst layer from falling off from the base material and increases the reverse current durability.

[0026] Furthermore, when the peak area of ​​X-rays diffracted by the (111) plane of the Pt metal in the catalytic layer is IPt and the peak area of ​​X-rays diffracted by the (200) and (111) planes of the Pt oxide is IPtO, the value of [IPt / (IPt+IPtO)] is preferably 0.1 or greater. This is because Pt oxide is electrochemically reduced to metal when subjected to hydrogen generating electrolysis, and a higher proportion of metal crystals from the beginning results in less morphological change in the catalytic layer and greater durability.

[0027] The lanthanoid element that becomes electrochemically stable as a trivalent ion within the potential window of water of pH 7 or higher and pH 16 or lower is not particularly limited, but from the viewpoint of keeping the cathode overvoltage low over a long period of time, it is preferably at least one element selected from the group consisting of La, Nd, Pm, Sm, Gd, Tb, and Dy, more preferably at least one element selected from the group consisting of Nd, Pm, Sm, Gd, and Dy, and particularly preferably Nd.

[0028] The material constituting the conductive substrate is not particularly limited, but is preferably a transition metal from the viewpoint of achieving both conductivity and durability. The transition metal is more preferably at least one selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Ru, Rh, Pd, Ag, Ir, Pt, and Au, even more preferably at least one selected from the group consisting of Ni, Ti, and Fe, and particularly preferably contains at least Ni. The conductive substrate may be made of a single transition metal, or an alloy or mixture of two or more transition metals, and may further contain, in addition to the transition metal, typical elements such as C, O, N, Si, P, and S.

[0029] The cathode of this embodiment is preferably a porous body in order to increase the surface area available for electrolysis and to efficiently remove gas generated by electrolysis from the electrode surface. In particular, in the case of a zero-gap electrolytic cell, it is necessary to degas the gas generated from the back side of the surface that comes into contact with the diaphragm, so it is preferable that the surface of the cathode opposite to the surface that comes into contact with the membrane is perforated. From this viewpoint, the form of the conductive substrate is not particularly limited, but is preferably a perforated metal, an expanded metal, a punched foil, a mesh woven with metal wires, a metal foam, a metal sintered body, a metal fiber, a metal paper, or the like, which has pores through which air bubbles can pass.

[0030] Furthermore, the effect of improving the reverse charge resistance described above is enhanced when the conductive substrate has a configuration without corners or protrusions, because corners or protrusions can become starting points for interfacial peeling between the catalyst layer and the substrate. Therefore, the conductive substrate is preferably a mesh made of metal wires that has no corners or protrusions, that is, a cross section perpendicular to the axial direction that is circular or elliptical. If the conductive substrate has corners or protrusions, such as expanded metal, the corners or protrusions may become the starting points for interfacial peeling of the catalyst layer, which may weaken the effect of improving reverse current durability of the present invention.

[0031] When a plain weave mesh is used for the conductive substrate, the dimensions are not particularly limited, but in order to achieve both an increase in the electrolytic reaction field due to an increase in the electrolytic surface area and efficient removal of gas generated by electrolysis from the electrode surface, the wire diameter is preferably 0.05 mm to 1.0 mm and the pitch is preferably 20 mesh to 60 mesh, more preferably 0.1 mm to 0.3 mm and the pitch is more preferably 30 mesh to 50 mesh.

[0032] When a foil is used as the conductive substrate, the dimensions are not particularly limited, but it is desirable for the foil to have flexibility in order to further enhance the effect of improving electrolysis efficiency due to the zero gap structure, and the thickness is preferably 100 μm or less, more preferably 60 μm or less, and still more preferably 40 μm or less.

[0033] Furthermore, the loading amount of the catalyst layer is 4.5 g / m 2 More than 20g / m 2 Preferably, it is 5.0 g / m or less. 2 More than 15g / m 2 More preferably, it is 6.0 g / m or less. 2 More than 10g / m 2 It is more preferable that the amount of the catalyst layer is 4.5 g / m or less. 2 By setting the amount of the catalyst layer to 20 g / m or more, it is possible to further reduce the overvoltage and further increase the reverse current durability. 2 This is because, by setting the thickness to the range below 1000 nm, it is possible to suppress peeling of the catalyst layer due to a decrease in the mechanical strength of the catalyst layer and an increase in overvoltage due to a decrease in the conductivity of the catalyst layer.

[0034] Furthermore, the catalyst layer contains Pt and a lanthanoid element, and preferably contains Pt, Nd as the lanthanoid element, and Ni. When the catalyst layer has a laminated structure, Pt and Ni the first layer containing Pt and Nd and the second layer containing

[0035] Furthermore, the amount of Pt element carried in the catalyst layer is 3.5 g / m 2 More than 15g / m 2 Preferably, it is 4.0 g / m or less. 2 More than 10g / m 2 More preferably, it is 5.0 g / m or less. 2 More than 7.0g / m 2 It is more preferable that the amount of Pt element carried in the catalyst layer is 3.5 g / m or less. 2 By setting the amount of Pt element carried in the catalyst layer at 15 g / m or more, it is possible to further reduce the overvoltage and further increase the durability against reverse current. 2 This is because, by setting the thickness to the range below 1000 nm, it is possible to suppress peeling of the catalyst layer due to a decrease in the mechanical strength of the catalyst layer and an increase in overvoltage due to a decrease in the conductivity of the catalyst layer.

[0036] Furthermore, the average thickness of the catalyst layer is not particularly limited, but is preferably 0.30 μm or more, because by making the average thickness of the catalyst layer 0.30 μm or more, cracks in the catalyst layer that run perpendicularly to the conductive substrate are reduced, the surface area of ​​the conductive substrate that comes into contact with the electrolyte is reduced, and peeling of the catalyst layer due to oxidation-reduction associated with reverse charging at the interface between the catalyst layer and the conductive substrate can be suppressed. On the other hand, if the average thickness of the catalyst layer is too large, the mechanical strength decreases and the catalyst layer becomes more susceptible to physical peeling, so the average thickness of the catalyst layer is preferably 10 μm or less. From the same viewpoint, the average thickness of the catalyst layer is more preferably 0.5 μm or more and 5 μm or less, and further preferably 0.7 μm or more and 4 μm or less.

[0037] Furthermore, it is more preferable that the catalytic layer contains a hydrogen storage alloy. By containing a hydrogen storage alloy, hydrogen generated by electrolysis is retained in the catalytic layer as atomic hydrogen. The reducing power of this atomic hydrogen promotes the reduction of the substrate oxide layer caused by forward current and suppresses the growth of the substrate oxide layer caused by reverse current, thereby suppressing morphological changes due to oxidation-reduction of the substrate and improving reverse current durability.

[0038] The hydrogen storage alloy is not particularly limited, but is preferably Pd in ​​view of electrochemical stability.

[0039] In addition, the cathode of this embodiment has a current density of 6 kA / m 2 After applying a reduction current of 15A / m for 1 hour 2 The cumulative discharge amount until the potential reaches +1.12 V (vs. RHE) is 1500 C / m 2 More than 10000C / m 2 When the cumulative discharge amount is within the above range, the rate at which the potential of the cathode shifts to the noble side due to the reverse current is slowed down, and the potential change stress on the cathode and the resulting deterioration can be reduced.

[0040] The effective area of ​​the cathode surface used for electrolysis can be determined in a pseudo manner by measuring the capacitance of the electric double layer formed at the interface between the cathode and the electrolyte. The electric double layer capacity can be measured by, for example, electrochemical impedance spectroscopy or cyclic voltammetry. In the former, the electric double layer capacity is calculated by analyzing a Cole-Cole plot, which is a plot of the real and imaginary parts obtained by AC impedance measurement, using equivalent circuit fitting. In the latter, cyclic voltammetry is measured at several levels of potential sweep rate in a potential region where no faradaic current is generated at the cathode, and the non-faradaic current value at a certain potential obtained is plotted against the sweep rate, and the electric double layer capacity is calculated from the slope of the plot.

[0041] The cathode of this embodiment has an electric double layer capacity of 0.001 F / cm calculated by cyclic voltammetry, from the viewpoint of increasing the effective area used for electrolysis and reducing the hydrogen generation overvoltage. 2 Furthermore, from the viewpoint of ensuring a sufficient electric double layer capacity to maintain a low overvoltage even if the catalyst is depleted or removed by a reverse current caused by the stop of forward current application, it is preferable that the electric double layer capacity calculated by cyclic voltammetry is 0.02 F / cm or more. 2 More preferably, it is 0.03 F / cm or less. 2 It is particularly preferable that the hardness is not less than 0.15 F / cm2.

[0042] Furthermore, the coating resistance of the cathode in this embodiment is 2 Ω·cm 2 Preferably it is equal to or less than 0.5 Ω cm, and more preferably it is 0.5 Ω cm 2 If the cathode film resistance is too high, the overvoltage increases when electrolysis is performed under high current density conditions in order to achieve high energy efficiency. The film resistance can be measured by, for example, electrochemical impedance spectroscopy. The film resistance is calculated by analyzing a Cole-Cole plot, which is a plot of the real and imaginary parts obtained by AC impedance measurement, using equivalent circuit fitting.

[0043] Examples of a method for producing the cathode by forming the catalytic layer on the conductive substrate include a plating method, a thermal spraying method such as a plasma spraying method, a thermal decomposition method in which a precursor layer solution is applied to the conductive substrate and then heat is applied, a method in which a catalytic substance is mixed with a binder component and then fixed to the substrate, and a vacuum film formation method such as a sputtering method.

[0044] The pyrolysis method allows a thin film of uniform thickness to be formed on a porous substrate, so that the surface of the conductive substrate can be efficiently coated with a small amount of raw material. The thermal decomposition method preferably includes a precursor layer forming step of forming a precursor layer on the surface of the conductive substrate, and a firing step of heating the conductive substrate having the precursor layer formed on its surface to decompose the precursor layer and form a catalyst layer.

[0045] The precursor layer forming step may be, for example, a method of applying a liquid containing a metal element to the surface of the substrate and drying it. Examples of the metal element include the aforementioned Pt, lanthanides, and Pt-group elements. The form of the metal in the coating solution is not particularly limited, and it may be in the form of fine particles of the metal or metal compound, or may be dissolved and ionized. In the case of fine particles, it is preferable that the metal is dispersed in the solution to form a homogeneous precursor layer. Therefore, the particle size is preferably 100 nm or less. In the case of ionized metal salts, examples include halide salts such as fluorides, chlorides, bromides, and iodides; inorganic compound salts such as nitrates, sulfates, and phosphates; and organic compound salts such as acetates. Among these, chlorides and nitrates are preferably used because the raw materials are industrially available. Furthermore, nitrates are more preferred because they cause little deterioration of the substrate due to the anionic components remaining after decomposition, allowing for the production of electrodes with good storage stability. The solvent for the solution may be any solvent capable of dissolving the solute, such as a metal salt. Since a high-concentration solution can be prepared, which increases the coating amount and improves productivity, it is preferable for the solution to contain at least one of water or an alcohol having 2 to 5 carbon atoms. If the concentration of the metal salt in the solution is low, a lot of energy is required to volatilize the solvent. On the other hand, if the concentration of the metal salt is high, unevenness may occur, resulting in an uneven thickness of the catalyst layer. Therefore, the concentration of the metal salt in the coating solution used in the precursor formation step is preferably 0.001 mol / L or more and 1 mol / L or less, more preferably 0.01 mol / L or more and 0.5 mol / L.

[0046] In the precursor layer forming step, various known methods can be used to apply the liquid containing a metal element to the surface of the conductive substrate. For example, a dip method in which the substrate is immersed in the liquid, a method in which the liquid is applied to the substrate with a brush, a roll method in which a liquid impregnated into a sponge roll is applied to the substrate, and an electrostatic application method in which the application liquid and the substrate are charged with opposite charges and sprayed using a spray or the like. In particular, the roll method and the electrostatic application method are preferably used from the viewpoints of productivity and the ability to uniformly apply the catalyst layer. The conductive substrate may be subjected to a surface treatment to provide irregularities on the surface prior to application of the solution. Providing irregularities on the substrate surface improves adhesion between the substrate and the catalyst layer. The surface treatment method is not particularly limited, and examples thereof include blasting and etching using a chemical solution.

[0047] The temperature at which the catalyst layer is formed in the calcination step may be equal to or higher than the thermal decomposition temperature of the metal salt used, but is preferably 300°C or higher. This is because the thermal decomposition of many metal salts proceeds at 300°C or higher. To ensure good thermal decomposition and removal of unreacted substances, the temperature is preferably 400°C or higher, more preferably 500°C or higher. Calcination at a temperature higher than 800°C may cause the substrate to soften and deform, so the temperature is preferably 800°C or lower, more preferably 600°C or lower.

[0048] It is preferable to repeat the precursor layer forming step and the calcination step multiple times. To form a catalyst layer of the desired thickness, the amount of liquid applied per time or the concentration of the metal salt in the liquid can be adjusted. However, if the amount of liquid applied per time or the metal concentration in the liquid is too high, unevenness may occur, and each layer may not be formed uniformly. Therefore, by repeating the precursor layer forming step and the calcination step multiple times, a more uniform catalyst layer of the desired thickness can be formed. The number of repetitions is not particularly limited as long as the desired thickness is obtained, but it is preferably 5 or more times.

[0049] After repeating the precursor layer forming step and the firing step multiple times, a firing step at a temperature equal to or higher than the temperature of the firing step may be further included. The upper limit of the firing temperature in this case is preferably 800°C or lower, more preferably 600°C or lower.

[0050] In this embodiment, the above-described features of the cathode for hydrogen generation and the cathode for alkaline water electrolysis may be used alone or in combination.

[0051] <Cathode manufacturing method> The method for producing the cathode of this embodiment is not particularly limited, and can be produced, for example, by the following production method. a coating step of coating the conductive substrate with a coating liquid containing at least a Pt compound and a lanthanoid compound; a precursor layer forming step of drying the coating liquid to form a precursor layer containing Pt and a lanthanoid on the conductive substrate; a calcination step of heating the precursor layer in a temperature range of 300°C to 800°C to obtain a catalyst layer; Repeating the steps in sequence two or more times; A method for manufacturing a cathode having the above structure.

[0052] The cathode of this embodiment can also be manufactured by the following manufacturing method. a first coating step of coating the conductive substrate with a first coating liquid containing at least a Pt compound and a lanthanoid compound; a first precursor layer forming step of drying the first coating liquid to form a first precursor layer containing Pt and a lanthanoid on the conductive substrate; a first firing step of heating the first precursor layer in a temperature range of 300°C to 800°C to obtain the first layer; After the first step, which is repeated two or more times in sequence, a second coating step of coating a second coating liquid containing at least a Pt compound and a lanthanoid compound in a molar ratio different from that of the first layer on the conductive substrate on which the first layer has been formed; a second precursor layer forming step of drying the second coating liquid to form a second precursor layer on the first layer, the second precursor layer containing Pt and a lanthanoid in a molar ratio different from that of the first layer; a second firing step of heating the second precursor layer in a temperature range of 300°C to 800°C to obtain a second layer; A method for manufacturing a cathode comprising repeating the second step two or more times in sequence.

[0053] Furthermore, the cathode of this embodiment can also be manufactured by the following manufacturing method. a first coating step of coating the conductive substrate with a first coating liquid containing at least a Pt compound and a lanthanoid compound; a first coating step of coating the conductive substrate containing Ni with a first coating liquid containing at least a Pt compound and Ni; a first precursor layer forming step of drying the first coating liquid to form a first precursor layer containing Pt and Ni on the conductive base material; a first firing step of heating the first precursor layer in a temperature range of 300°C to 800°C to obtain the first layer; After the first step, which is repeated two or more times in sequence, a second coating step of coating a second coating liquid containing at least a Pt compound and an Nd compound onto the conductive substrate on which the first layer has been formed; a second precursor layer forming step of drying the second coating liquid to form a second precursor layer containing Pt and Nd on the first coating layer; a second firing step of heating the second precursor layer in a temperature range of 300°C to 800°C to obtain a second layer; A method for manufacturing a cathode comprising repeating the second step two or more times in sequence.

[0054] <Bipolar electrolytic cell, alkaline water electrolysis cell> The bipolar electrolytic cell of this embodiment is characterized by including the cathode of this embodiment described above. By providing the cathode of this embodiment, even when hydrogen generation is repeatedly started and stopped, the overvoltage does not increase and high energy conversion efficiency can be maintained for a long period of time.

[0055] The alkaline water electrolysis cell of this embodiment includes 3 to 200 bipolar electrolytic cells of this embodiment, at least one cathode terminal cell, and at least one anode terminal cell. By configuring an electrolytic cell from the alkaline water electrolysis cell of this embodiment, even when hydrogen generation is repeatedly started and stopped, the overvoltage does not increase and high energy conversion efficiency can be maintained for a long period of time.

[0056] FIG. 1 shows a side view of an example of an entire electrolytic cell for alkaline water electrolysis including a bipolar electrolytic cell according to the present embodiment. FIG. 2 shows a diagram of the zero gap structure of an example of an electrolytic cell for alkaline water electrolysis including the bipolar electrolytic cell of this embodiment (a cross-sectional view of the portion enclosed by the dashed square frame in FIG. 1). As shown in Figs. 1 and 2 , the alkaline water electrolysis cell 50 of this embodiment is preferably an alkaline water electrolysis cell in which a plurality of elements 60, each including an anode 2a, a cathode 2c, a partition wall 1 separating the anode 2a and the cathode 2c, and an outer frame 3 bordering the partition wall 1, are stacked one on top of the other with a diaphragm 4 sandwiched between them.

[0057] In the alkaline water electrolysis cell 50 of this embodiment, the diaphragm 4 is in contact with the anode 2a and the cathode 2c, forming a zero-gap structure Z (see FIG. 2).

[0058] The electrolytic cell for alkaline water electrolysis of this embodiment may be a monopolar type or a bipolar type, and is preferably an electrolytic cell for alkaline water electrolysis in which bipolar elements are stacked with a diaphragm interposed therebetween. The monopolar type is a method in which one or more elements are each directly connected to a power source, while the bipolar type is a method in which multiple bipolar elements are arranged in series and the elements at both ends are connected to a power source.

[0059] In this embodiment, as shown in FIG. 1, an alkaline water electrolysis cell 50 is configured by stacking a required number of bipolar elements 60. In the example shown in FIG. 1 , the alkaline water electrolysis cell 50 includes a fast head 51g, an insulating plate 51i, and an anode terminal element 51a arranged in this order from one end. Furthermore, the anode side gasket portion, the diaphragm 4, the cathode side gasket portion, and the bipolar element 60 are arranged in this order. The bipolar element 60 is arranged so that the cathode 2c faces the anode terminal element 51a. The anode gasket through the bipolar element 60 are arranged repeatedly as many times as necessary for the designed production volume. After the necessary number of anode gaskets through the bipolar element 60 are arranged repeatedly, the anode side gasket portion, the diaphragm 4, and the cathode side gasket portion are again arranged in this order. Finally, the cathode terminal element 51c, the insulating plate 51i, and the loose head 51g are arranged in this order. The alkaline water electrolysis cell 50 is assembled by fastening the entire assembly with tie rods 51r to form the alkaline water electrolysis cell 50. The arrangement of the alkaline water electrolysis cell 50 can be arbitrarily selected from either the anode side or the cathode side, and is not limited to the above-mentioned order.

[0060] As shown in FIG. 1 , in an alkaline water electrolysis cell 50, a bipolar element 60 is disposed between an anode terminal element 51 a and a cathode terminal element 51 c, and diaphragms 4 are disposed between the anode terminal element 51 a and the bipolar element 60, between adjacent bipolar elements 60, and between the bipolar element 60 and the cathode terminal element 51 c.

[0061] In the alkaline water electrolysis cell 50 of this embodiment, as shown in FIG. 2, the diaphragm 4 is in contact with the anode 2a and the cathode 2c, forming a zero-gap structure Z. In this embodiment, in particular, the portion between the partition walls 1 between two adjacent bipolar elements 60 and the portion between the partition walls 1 between an adjacent bipolar element 60 and a terminal element in the alkaline water electrolysis cell 50 are referred to as the electrolytic cell 65. The electrolytic cell 65 includes the partition wall 1, anode chamber 5a, anode 2a, and diaphragm 4 of one element, and the cathode 2c, cathode chamber 5c, and partition wall 1 of the other element.

[0062] In alkaline water electrolysis, if there is a gap between the diaphragm 4 and the anode 2a or the cathode 2c, a large amount of gas bubbles generated during electrolysis will accumulate in this area in addition to the electrolyte, resulting in a very high electrical resistance. In order to significantly reduce the electrolysis voltage in the electrolytic cell 65, it is effective to make the distance between the anode 2a and the cathode 2c (hereinafter also referred to as the "inter-electrode distance") as small as possible to eliminate the influence of the electrolyte and gas bubbles present between the anode 2a and the cathode 2c.

[0063] Therefore, a zero gap structure is adopted, which can maintain a state in which the anode 2a and the diaphragm 4 are in contact with each other and the cathode 2c and the diaphragm 4 are in contact with each other over the entire electrode surface, or a state in which the inter-electrode distance is substantially the same as the thickness of the diaphragm 4 and there is almost no gap between the anode 2a and the diaphragm 4 and between the cathode 2c and the diaphragm 4 over the entire electrode surface.

[0064] In the alkaline water electrolysis cell 50 of this embodiment, as shown in FIG. 2, the partition wall 1, the outer frame 3, and the diaphragm 4 define an electrode chamber 5 through which the electrolytic solution passes. The header pipes, which are pipes for distributing or collecting the electrolytic solution and are attached to the alkaline water electrolysis cell 50 shown in Figs. 1 and 2, are typically of an internal header type or an external header type, but either type may be employed in the present invention, and there is no particular limitation thereon.

[0065] The components of the bipolar electrolytic cell and alkaline water electrolysis cell of this embodiment will be described in detail below. In addition, preferred embodiments for enhancing the effects of the present invention will be described in detail below.

[0066] (bulkhead) The partition wall 1 is preferably provided between the cathode 2c and the anode 2a, between the anode 2a and the cathode current collector 2r and / or between the cathode 2c and the anode current collector 2r. The shape of the partition wall in this embodiment may be a plate shape having a predetermined thickness, but is not particularly limited to this. The shape of the partition wall in plan view is not particularly limited, and may be rectangular (square, oblong, etc.) or circular (circle, ellipse, etc.), and the rectangle may have rounded corners.

[0067] The size of the partition wall is not particularly limited and may be designed appropriately depending on the size of the electrode chamber. Moreover, as the material of the partition wall, a material having high electrical conductivity is preferable from the viewpoint of realizing a uniform supply of power, and nickel, a nickel alloy, mild steel, or a nickel alloy plated with nickel is preferable from the viewpoint of alkali resistance and heat resistance.

[0068] (electrode) The size of the electrode is not particularly limited and may be determined according to the size of the electrode chamber, and may be 0.4 m to 4.0 m in length, 0.4 m to 6.0 m in width, and 0.1 mm to 3 mm in thickness.

[0069] In the bipolar electrolytic cell of this embodiment, at least one of the anode and cathode is preferably porous, and more preferably both the anode and the cathode are porous, in order to increase the surface area used for electrolysis and to efficiently remove gas generated by electrolysis from the electrode surface. In particular, in the case of a zero-gap electrolytic cell, it is necessary to degas the gas generated from the back side of the surface in contact with the diaphragm, so it is preferable that the surface of the electrode opposite to the surface in contact with the membrane is perforated.

[0070] The anode preferably includes a porous metal body, since the catalyst layer carried on the electrode is porous, increasing the effective electrolysis area and enabling a lower voltage.

[0071] Examples of porous bodies include plain weave and twill weave meshes, punched metals, expanded metals, and metal foams.

[0072] When a perforated metal is used, the dimensions are not particularly limited. However, in order to achieve both an increase in the amount of gas generated due to an increase in the electrolysis surface area and efficient removal of the gas generated by electrolysis from the electrode surface, and from the viewpoint of mechanical strength, it is preferable that the hole diameter be 2 mm or more and 8 mm or less, the pitch be 2 mm or more and 10 mm or less, the opening ratio be 20% or more and 80% or less, and the thickness be 0.5 mm or more and 2 mm or less.

[0073] When an expanded metal is used, the dimensions are not particularly limited, but in order to achieve both an increase in the amount of gas generated due to an increase in the electrolysis surface area and efficient removal of the gas generated by electrolysis from the electrode surface, and from the standpoint of mechanical strength, it is preferable that the center-to-center distance in the short direction of the mesh (SW) be 2 mm or more and 5 mm or less, the center-to-center distance in the long direction of the mesh (LW) be 3 mm or more and 10 mm or less, the thickness be 0.5 mm or more and 2 mm or less, and the opening ratio be 20% or more and 80% or less.

[0074] When a metal foam is used, the dimensions are not particularly limited. However, in order to achieve both an increase in the amount of gas generated due to an increase in the electrolysis surface area and efficient removal of the gas generated by electrolysis from the electrode surface, and from the viewpoint of mechanical strength, it is preferable that the porosity be 80% or more and 95% or less, and the thickness be 0.5 mm or more and 2.0 mm or less.

[0075] The material of the substrate is not particularly limited, but in view of resistance to the use environment, it is preferable that the substrate contains mild steel, stainless steel, Ni, or a Ni-based alloy, and more preferably contains Ni.

[0076] The anode has holes, and the aperture ratio is preferably 30% or more and 70% or less in order to efficiently remove gas generated by electrolysis from the anode surface.

[0077] The catalytic layer of the anode preferably has high oxygen generation capacity, and Ni, Co, Fe, or Pt group elements can be used. To achieve the desired activity and durability, the catalytic layer can be formed as a simple metal, a compound such as an oxide, a composite oxide or alloy consisting of multiple metal elements, or a mixture thereof. Specific examples include Ni plating, alloy plating of Ni and Co, Ni and Fe, composite oxides containing Ni and Co such as LaNiO3, LaCoO3, and NiCo2O4, compounds of Pt group elements such as iridium oxide, and carbon materials such as graphene. Organic materials such as polymers may also be included to improve durability and adhesion to the substrate.

[0078] (Outer frame) The shape of the outer frame 3 in the bipolar electrolytic cell of the present embodiment is not particularly limited as long as it can frame the partition wall 1; however, the outer frame 3 may have a shape that includes an inner surface extending along a direction perpendicular to the plane of the partition wall 1, over the entire periphery of the partition wall 1. The shape of the outer frame is not particularly limited and may be determined appropriately in accordance with the shape of the partition wall in a plan view. The dimensions of the outer frame are not particularly limited and may be designed according to the outer dimensions of the electrode chamber.

[0079] The material for the outer frame is preferably a conductive material, and from the standpoint of alkali resistance and heat resistance, nickel, nickel alloy, mild steel, or nickel alloy plated with nickel is preferred.

[0080] (diaphragm) The diaphragm 4 used in the bipolar electrolytic cell 65 of this embodiment is an ion-permeable diaphragm that separates the generated hydrogen gas and oxygen gas while conducting ions. This ion-permeable diaphragm can be an ion exchange membrane with ion exchange capacity or a porous membrane that is permeable to the electrolytic solution. This ion-permeable diaphragm preferably has low gas permeability, high ionic conductivity, low electronic conductivity, and high strength.

[0081] The porous membrane has a structure with multiple fine through-holes that allows the electrolyte to pass through the membrane. Since the electrolyte penetrates the porous membrane to exhibit ionic conduction, it is extremely important to control the porous structure, such as pore size, porosity, and hydrophilicity. On the other hand, it is also required to not only allow the electrolyte to pass through, but also the generated gas, i.e., to have gas barrier properties. From this perspective, control of the porous structure is also important.

[0082] The porous membrane has a plurality of fine through-holes, and examples thereof include polymer porous membranes, inorganic porous membranes, woven fabrics, nonwoven fabrics, etc. These can be produced by known techniques.

[0083] Ion exchange membranes include cation exchange membranes that selectively allow cations to pass through and anion exchange membranes that selectively allow anions to pass through, and either type of exchange membrane can be used. The material of the ion exchange membrane is not particularly limited, and known materials can be used. For example, fluorine-containing resins and modified resins of polystyrene-divinylbenzene copolymers are preferably used. Fluorine-containing ion exchange membranes are particularly preferred because of their excellent heat resistance and chemical resistance.

[0084] Furthermore, in the zero-gap electrolytic cell 65, a spring, which is an elastic body 2e, is preferably disposed between the electrode 2 and the partition wall 1 as a means for reducing the interelectrode distance, and the electrode is preferably supported by this spring. For example, in a first example, a spring made of a conductive material may be attached to the partition wall 1, and the electrode 2 may be attached to this spring. In a second example, a spring may be attached to the electrode rib 6 attached to the partition wall 1, and the electrode 2 may be attached to this spring. Note that when such a configuration using an elastic body is adopted, the strength, number, shape, and the like of the spring must be appropriately adjusted as necessary to prevent uneven contact pressure between the electrode and the diaphragm.

[0085] In addition, by increasing the rigidity of the other electrode that is paired with the electrode supported via the elastic body (for example, by making the anode more rigid than the cathode), a structure is achieved that is less likely to deform when pressed. On the other hand, by making the electrode supported via the elastic body a flexible structure that deforms when the diaphragm is pressed, it is possible to absorb unevenness due to tolerances in the manufacturing precision of the electrolytic cell and deformation of the electrodes, thereby maintaining the zero gap structure.

[0086] The zero gap structure Z may be a zero gap structure formed between the anode terminal element 51a and an element, between elements, or between an element and the cathode terminal element 51c. 2, in the bipolar electrolytic cell 65 of this embodiment, a conductive elastic body 2e and a cathode current collector 2r are preferably provided between the cathode 2c and the partition wall 1 such that the conductive elastic body 2e is sandwiched between the cathode 2c and the cathode current collector 2r. In addition, the cathode current collector 2r is preferably in contact with the rib 6 of the cathode.

[0087] As illustrated in FIG. 2 , the zero gap structure Z of the bipolar electrolytic cell 65 of the present embodiment preferably has a structure in which a bipolar element 60 is stacked with the anode rib 6 and the anode 2a stacked in this order on the anode 2a side of the partition wall 1, and the cathode rib 6, the cathode current collector 2r, the conductive elastic body 2e, and the cathode 2c stacked in this order on the cathode 2c side of the partition wall 1, with the diaphragm 4 sandwiched between them, and the diaphragm 4 is in contact with the anode 2a and the cathode 2c.

[0088] (current collector) Examples of the current collector include a cathode current collector and an anode current collector. The current collector not only transmits electricity to the conductive elastic body and electrodes stacked thereon, but also supports the loads received from them and allows gas generated from the electrodes to pass through to the partition wall side without hindrance. Therefore, the shape of this current collector is preferably an expanded metal or a perforated plate. In this case, the aperture ratio of the current collector is preferably within a range that allows hydrogen gas generated from the electrodes to be released to the partition wall side without hindrance. However, if the aperture ratio is too large, problems such as a decrease in strength or a decrease in conductivity to the conductive elastic body may occur, while if the aperture ratio is too small, gas escape may be poor.

[0089] As the material for the current collector, nickel, nickel alloy, stainless steel, mild steel, etc. can be used from the viewpoints of electrical conductivity and alkali resistance, but nickel, mild steel, or stainless steel-nickel alloy plated with nickel is preferred from the viewpoint of corrosion resistance.

[0090] (Conductive elastic body) The conductive elastic body is located between the current collector and the electrode and is in contact with both the current collector and the electrode. It is essential that it transmits electricity to the electrode and does not inhibit the diffusion of gas generated from the electrode. Impeding gas diffusion increases electrical resistance and reduces the electrode area used for electrolysis, thereby reducing the electrolysis efficiency. Its most important role is to apply an appropriate amount of pressure evenly to the electrode without damaging the diaphragm, thereby ensuring close contact between the diaphragm and the electrode.

[0091] (electrode chamber) In an alkaline water electrolysis cell 50 according to this embodiment, as shown in Fig. 2, electrode chambers 5, through which the electrolytic solution passes, are defined by a partition wall 1, an outer frame 3, and a diaphragm 4. The electrode chamber 5 on the anode side across the partition wall 1 is an anode chamber 5a, and the electrode chamber 5 on the cathode side is a cathode chamber 5c.

[0092] (rib) In the bipolar electrolytic cell 65 of this embodiment, the rib 6 is preferably physically connected to the electrode 2. With such a configuration, the rib 6 serves as a support for the electrode 2, making it easier to maintain the zero-gap structure Z. In addition, the rib 6 is preferably electrically connected to the partition wall 1. In the above-described example of a bipolar electrolytic cell, a structure is adopted in the cathode chamber, in which the cathode rib-cathode current collector-conductive elastic body-cathode are stacked in this order, and a structure is adopted in the anode chamber, in which the anode rib-anode are stacked in this order. However, the present invention is not limited to this structure, and the anode chamber may also have an "anode rib-anode current collector-conductive elastic body-anode" structure.

[0093] The ribs are generally made of a conductive metal, such as nickel-plated mild steel, stainless steel, or nickel. The ribs are preferably made of the same material as the partition walls, and nickel is most preferred.

[0094] (gasket) In the bipolar electrolytic cell 65 of this embodiment, as shown in FIG. 2, it is preferable that a gasket 7 is sandwiched together with the diaphragm 4 between the outer frames 3 that frame the partition walls 1. The gasket 7 is used to seal the space between the bipolar element 60 and the diaphragm 4 and between the bipolar elements 60 against the electrolyte and the generated gas, and can prevent leakage of the electrolyte or the generated gas to the outside of the electrolytic cell and mixing of gases between the two electrode chambers.

[0095] A typical gasket structure is a square or annular shape with the electrode surface hollowed out to match the surface of the element (such as a bipolar element, an anode terminal element, or a cathode terminal element) that contacts the frame. Diaphragms can be stacked between elements by sandwiching them between two such gaskets. Furthermore, the gasket preferably has a slit that can accommodate the diaphragm so that it can hold the diaphragm, and also has openings that allow the accommodated diaphragm to be exposed on both surfaces of the gasket. This allows the gasket to accommodate the edge of the diaphragm within the slit, covering the edge faces of the diaphragm. This more reliably prevents electrolyte and gas from leaking from the edge faces of the diaphragm.

[0096] The material of the gasket is not particularly limited, and known insulating rubber materials, resin materials, etc. can be selected. Examples of rubber and resin materials that can be used include natural rubber (NR), styrene-butadiene rubber (SBR), chloroprene rubber (CR), butadiene rubber (BR), acrylonitrile-butadiene rubber (NBR), silicone rubber (SR), ethylene-propylene rubber (EPT), ethylene-propylene-diene rubber (EPDM), fluororubber (FR), isobutylene-isoprene rubber (IIR), urethane rubber (UR), and chlorosulfonated polyethylene rubber (CSM). Fluororesin materials include polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-ethylene copolymer (ETFE), and chlorotrifluoroethylene-ethylene copolymer (ECTFE). Resin materials include polyphenylene sulfide (PPS), polyethylene, polyimide, and polyacetal. Among these, ethylene-propylene-diene rubber (EPDM) and fluororubber (FR) are particularly suitable in terms of elastic modulus and alkali resistance.

[0097] (Header) The alkaline water electrolysis cell preferably has a cathode chamber and an anode chamber for each electrolysis cell. In order to continuously perform the electrolysis reaction in the electrolysis cell, it is necessary to continuously supply an electrolyte containing a sufficient amount of raw materials to be consumed by electrolysis to the cathode chamber and the anode chamber of each electrolysis cell.

[0098] The electrolytic cells are connected to electrolyte supply and discharge pipes called headers, which are common to multiple electrolytic cells. Generally, the anode distribution pipe is called the anode inlet header, the cathode distribution pipe is called the cathode inlet header, the anode collection pipe is called the anode outlet header, and the cathode collection pipe is called the cathode outlet header. The elements are connected to each electrolyte distribution pipe and each electrolyte collection pipe via hoses, etc.

[0099] The material of the header is not particularly limited, but it is necessary to use a material that can adequately withstand the corrosiveness of the electrolyte used and the operating conditions such as pressure and temperature. Materials that may be used for the header include iron, nickel, cobalt, PTFE, ETFE, PFA, polyvinyl chloride, polyethylene, etc.

[0100] The internal header type refers to a type in which the alkaline water electrolysis cell and the header (a pipe for distributing or collecting the electrolyte) are integrated. In an example of the internal header type, an anode inlet header and a cathode inlet header are provided in a part of a lower portion of an outer frame at the end edge of the partition wall, and similarly, an anode outlet header and a cathode outlet header are provided in a part of an upper portion of the outer frame at the end edge of the partition wall. The outer frame and the anode chamber or the cathode chamber are connected by an electrolyte inlet or electrolyte outlet through which the electrolyte passes.

[0101] The external header type refers to a type in which the alkaline water electrolysis cell and the header (the pipe for distributing or collecting the electrolyte) are independent. In an external header type alkaline water electrolysis cell, an anode inlet header and a cathode inlet header are provided independently, running parallel to the electrolytic cell in a direction perpendicular to the current-carrying surface of the electrolytic cell. The anode inlet header and cathode inlet header are connected to each element by hoses.

[0102] The internal header type and external header type electrolytic cells for alkaline water electrolysis may have therein a gas-liquid separation box that separates the gas generated by electrolysis from the electrolytic solution. The installation position of the gas-liquid separation box is not particularly limited, and the box may be installed between the anode chamber and the anode outlet header or between the cathode chamber and the cathode outlet header.

[0103] (electrolyte) In the alkaline water electrolysis cell of this embodiment, a cathode chamber frame with a cathode attached thereto and an anode chamber frame with an anode attached thereto are arranged with a partition wall between them. That is, the anode chamber and the cathode chamber are separated by the partition wall. The electrolytic solution is supplied to the anode chamber and the cathode chamber. The electrolyte can be one generally used for water electrolysis. Examples include an aqueous solution of potassium hydroxide and an aqueous solution of sodium hydroxide. The electrolyte concentration is preferably 1N or more and 12N or less, and more preferably 6N or more and 10N or less.

[0104] The alkaline water electrolysis cell of this embodiment includes the anode and cathode as described above, and an electrolytic solution is circulated through the electrolytic cell. A current is applied to the electrolytic cell to perform water electrolysis, thereby producing hydrogen at the cathode. A variable power supply, for example, can be used as the power source. A variable power supply is a power supply derived from a renewable energy power plant whose output fluctuates over a period of several seconds to several minutes, unlike power supplies that provide a stable output, such as grid power. The method of generating renewable energy is not particularly limited, and examples include solar power generation and wind power generation. For example, in the case of electrolysis using an alkaline water electrolysis cell, cationic electrolytes in the electrolytic solution migrate from the anode chamber of one element through the diaphragm to the cathode chamber of an adjacent element, and anionic electrolytes migrate from the cathode chamber of one element through the diaphragm to the anode chamber of the adjacent element. Therefore, current during electrolysis flows in the direction in which the elements are connected in series. That is, current flows from the anode chamber of one element to the cathode chamber of the adjacent element through the diaphragm. During electrolysis, oxygen gas is produced in the anode chamber and hydrogen gas is produced in the cathode chamber.

[0105] The bipolar electrolytic cell 65 of this embodiment can be used in a bipolar electrolytic cell 50, an electrolysis device 70 for alkaline water electrolysis, etc. Examples of the electrolysis device 70 for alkaline water electrolysis include a device including the bipolar electrolytic cell 50 of this embodiment, a liquid feed pump 71 for circulating the electrolytic solution, a gas-liquid separation tank 72 for separating the electrolytic solution from hydrogen and / or oxygen, and a water supply device for supplying water consumed by electrolysis. The alkaline water electrolysis apparatus 70 may further include a rectifier 74, an oxygen concentration meter 75, a hydrogen concentration meter 76, a flow meter 77, a pressure meter 78, a heat exchanger 79, a pressure control valve 80, and the like.

[0106] In the alkaline water electrolysis method using the alkaline water electrolysis apparatus, the current density applied to the electrolytic cell is 1 kA / m 2 ~20kA / m 2 Preferably, it is 6 kA / m 2 ~15kA / m 2 It is more preferable that: In particular, when a variable power supply is used, it is preferable to set the upper limit of the current density within the above range.

[0107] In the bipolar electrolytic cell of this embodiment, the alkaline water electrolysis anode is supplied with a current of 6 kA / m 2 After applying an oxidation current of 15 A / m² for 1 hour, a reduction current of 15 A / m² is applied, and the cumulative discharge amount until the potential reaches +0.12 V (vs. RHE) is 6 kA / m² to the cathode for hydrogen generation. 2 After applying a reduction current of 15A / m for 1 hour 2 It is preferable that the cumulative discharge amount is greater than the cumulative discharge amount required to pass an oxidation current of +1.12 V (vs. RHE) when the potential reaches +1.12 V. This makes the potential fluctuation due to reverse current smaller at the anode than at the cathode, suppressing deterioration of the anode due to reverse current and allowing the cell voltage to be maintained at a lower level.

[0108] From the above viewpoint, the anode is supplied with 6 kA / m 2 After applying an oxidation current of 15A / m for 1 hour 2 The cumulative discharge amount until the potential reaches +0.12V (vs. RHE) is 10,000C / m 2 More than 300000C / m 2 It is preferable that:

[0109] <Hydrogen production method> The hydrogen production method of the present embodiment involves electrolyzing alkali-containing water in an electrolytic cell to produce hydrogen, and can be carried out using the alkaline water electrolysis cell of the present embodiment.

[0110] The details of the alkaline water electrolysis cell of this embodiment are as described above. In the hydrogen production method of the present embodiment, hydrogen can be produced by electrolyzing water containing alkali using a variable power supply that involves repeating positive current application and interruption of positive current application.

[0111] The cathode for hydrogen generation according to the embodiment of the present invention, the bipolar electrolytic cell according to the embodiment of the present invention, the electrolytic cell for alkaline water electrolysis according to the embodiment of the present invention, and the hydrogen production method according to the embodiment of the present invention have been illustrated and described with reference to the drawings, but these are not limited to the above examples, and appropriate modifications can be made to the above embodiments. [Example]

[0112] The present invention will be described below with reference to specific examples and comparative examples, but the present invention is not limited to the following examples.

[0113] (Example 1-1) A bipolar element was fabricated according to the following steps to be used as Example 1-1.

[0114] -Cathode 1- The conductive substrate was a plain-woven mesh substrate made of nickel fine wires with a diameter of 0.15 mm woven at a mesh size of 40. The conductive substrate was blasted with alumina powder having a weight-average particle size of 100 μm or less, and then cut into a size of 8.5 cm × 17.0 cm. The substrate was then acid-treated in 6N hydrochloric acid at room temperature for 10 minutes, washed with water, and dried. The dried conductive substrate was heated and sintered in a muffle furnace at 500°C for 10 minutes to form a nickel oxide layer on the surface of the conductive substrate. The weight of the conductive substrate after heating and sintering was measured using a PG503-S electronic balance manufactured by Mettler-Toledo K.K. Next, dinitrodiammine platinum nitric acid solution (Tanaka Precious Metals, Pt concentration: 100 g / L), neodymium nitrate hexahydrate (Kanto Chemical, 3N5), and water were mixed so that the molar ratio of platinum element to neodymium element was 70:30, to prepare coating solution 1.

[0115] -Coating process- The conductive substrate after heating and baking was immersed in a tray containing coating liquid 1, then removed, and an air blower was used to wipe off the coating liquid that had accumulated in the mesh of the conductive substrate (dip method).

[0116] -Precursor layer formation process- The conductive substrate that had been subjected to the coating step was dried at 60° C. for 10 minutes to form a precursor layer.

[0117] -Firing process- The conductive substrate on which the precursor layer had been formed was heated and baked in a muffle furnace at 500° C. for 10 minutes to pyrolyze the precursor layer. This cycle of the dip coating step, precursor layer forming step, and firing step was repeated 17 times, followed by post-firing at 500° C. for 1 hour in an air atmosphere to produce cathode 1. The weight of the cathode 1 was measured using an electronic balance, and the difference between the weight of the cathode 1 and the weight of the conductive substrate before the formation of the catalyst layer was divided by the area of ​​8.5 cm×17.0 cm to calculate the weight of the catalyst layer per unit area. The weight of the catalyst layer was then calculated assuming that the weight of the catalyst layer was the total weight of PtO and Nd2O3 contained in the catalyst layer.

[0118] -Anode 1- A Ni expanded metal having a SW of 3.0 mm, a LW of 4.5 mm, a thickness of 0.75 mm, and an aperture ratio of 54% was used as the anode 1.

[0119] -Partition walls, outer frames- The bipolar element used had a partition wall separating the anode and cathode and an outer frame surrounding the partition wall. All of the materials used for the partition wall and the frame of the bipolar element, which come into contact with the electrolyte, were nickel.

[0120] -Conductive elastic body- The conductive elastic body was made of woven nickel wire with a diameter of 0.15 mm, which was corrugated to a wave height of 5 mm. It was 5 mm thick, had a resilience of 150 g / cm2 at 50% compression deformation, and had a mesh size of approximately 5 meshes.

[0121] -diaphragm- 135 g of zirconium oxide (trade name "EP Zirconium Oxide," manufactured by Daiichi Kigenso Kagaku Kogyo Co., Ltd.) and 210 g of N-methyl-2-pyrrolidone (manufactured by Wako Pure Chemical Industries, Ltd.) were placed in a 1000 mL ball mill pot containing 1 kg of 0.5 mm diameter SUS balls. The mixture was stirred at 70 rpm in a 25°C atmosphere for 3 hours to disperse the mixture, yielding a mixture. The resulting mixture was filtered through a stainless steel sieve (30 mesh) to separate the balls from the mixture. 45 g of polysulfone ("Udel" (registered trademark), manufactured by Solvay Advanced Polymers) and 18 g of polyvinylpyrrolidone (weight average molecular weight (Mw) 900,000, manufactured by Wako Pure Chemical Industries, Ltd.) were added to the mixture from which the balls were separated, and the mixture was stirred and dissolved at 60°C for 12 hours using a Three-One motor to obtain a coating solution with the following composition. Polysulfone: 15 parts by mass Polyvinylpyrrolidone: 6 parts by mass N-methyl-2-pyrrolidone: 70 parts by mass Zirconium oxide: 45 parts by mass The above coating solution was applied to both surfaces of a polyphenylene sulfide mesh substrate (manufactured by Kureha Corporation, film thickness 280 μm, mesh size 358 μm, fiber diameter 150 μm) using a comma coater to a coating thickness of 150 μm on each side. Immediately after coating, the substrate coated with the coating solution was exposed to steam from a coagulation bath containing a 30°C pure water / isopropanol mixture (manufactured by Wako Pure Chemical Industries, Ltd., pure water / isopropanol = 50 / 50 (v / v)) for 2 minutes. Immediately thereafter, the substrate coated with the coating solution was immersed in the coagulation bath for 4 minutes. Then, a coating film was formed on the surface of the substrate by coagulating the polysulfone. The coating film was then thoroughly washed with pure water to obtain a porous membrane. The average pore size of this porous membrane was 0.3 μm in terms of water permeability at 90°C. The thickness was 580 μm. The porosity was 43%. The mode diameter of ZrO2 was 5.0 μm. The ratio of the mode diameter of the inorganic particles to the average pore size of the porous membrane (mode diameter / average pore size) was 2.6.

[0122] -gasket- The gasket used was a square with a thickness of 4.0 mm, a width of 18 mm, and an inner dimension of 504 mm square. It had an opening on the inside that was the same dimensions as the electrode chamber in a plan view, and a slit structure for inserting and holding a diaphragm. The slit structure had a 0.4 mm gap in the center of the thickness direction of the inner wall of the opening, for inserting and holding a diaphragm. This gasket was made of EPDM rubber, and had a tensile stress of 4.0 MPa at 100% deformation.

[0123] -Zero-gap type multi-pole element- The external header type zero gap cell unit 60 was a rectangle measuring 540 mm x 620 mm, and the area of ​​the current-carrying surfaces of the anode 2a and cathode 2c was 500 mm x 500 mm. The cathode side of the zero gap bipolar element 60 was composed of a laminate of the cathode 2c, conductive elastic body 2e, and cathode current collector 2r, and was connected to the partition wall 1 via the cathode rib 6, forming a cathode chamber 5c through which the electrolyte flows. The anode side was composed of the anode 2a connected to the partition wall 1 via the anode rib 6, forming an anode chamber 5a through which the electrolyte flows (Figures 3 and 4). The depth of the anode chamber 5a (anode chamber depth, the distance between the partition wall and the anode in FIG. 4) was 25 mm, and the depth of the cathode chamber 5c (cathode chamber depth, the distance between the partition wall and the cathode current collector in FIG. 4) was 25 mm, and they were made of nickel. The thickness of the nickel partition wall 1 to which the nickel anode rib 6 with a height of 25 mm and a thickness of 1.5 mm and the nickel cathode rib 6 with a height of 25 mm and a thickness of 1.5 mm were attached by welding was 2 mm. The cathode current collector 2r was a nickel expand substrate that had been pre-blasted. The substrate had a thickness of 1 mm and an aperture ratio of 54%. The conductive elastic body 2e was fixed onto the cathode current collector 2r by spot welding. In addition, as shown in Figure 5, a nozzle 9a leading to the cathode chamber was provided on the side of the element for the area X enclosed by the dashed line in Figure 4. A PFA-coated Pt wire 8 was inserted into an EPDM disk 9d and a PTFE disk 9c, each of which had a hole in the center that matched the diameter of the PFA-coated Pt wire 8. The Pt wire was then inserted into the nozzle 9a, and the EPDM disk d and the PTFE disk 9c were fastened together with a cap nut 9b. This configuration allowed the PFA-coated Pt wire to be introduced into the cell without leaking electrolyte. The PFA coating on one end of the PFA-coated Pt wire 8, approximately 10 mm long, was peeled off from the outside of the element so that the Pt wire 8 could be grasped with an alligator clip. Furthermore, for area Y enclosed by the two-dot dashed line in Figure 4, as shown in Figure 6, the PFA coating of the Pt wire a introduced into the cathode chamber of the element was peeled off by about 0.5 mm so that the Pt wire would come into contact with the hydrogen bubbles generated by electrolysis. This PFA-coated Pt wire a was bent inside the cathode chamber and passed through the through-hole of the current collector 2r and the gap between the conductive elastic body 2e, near the surface of the cathode 2c(2) opposite the diaphragm. The tip of the Pt wire was fixed so that it did not come into contact with the cathode 2c(2), the conductive elastic body 2e, or the current collector 2r (Figure 6). This allowed the Pt wire to come into contact with the hydrogen bubbles generated by electrolysis, forming an RHE reference electrode whose potential was at the hydrogen generation potential. By stacking these zero-gap type bipolar elements via a gasket that holds the diaphragm, a zero-gap structure Z can be formed in which the anode 2 a and the cathode 2 c are pressed against the diaphragm 4 .

[0124] (Example 1-2) A bipolar element was prepared as Example 1-2 under the same conditions as in Example 1-1, except that a cathode 2 prepared as described below was used. -Cathode 2- The conductive substrate was a plain-woven mesh substrate made of nickel fine wires with a diameter of 0.15 mm woven at a mesh size of 40. The conductive substrate was blasted with alumina powder having a weight-average particle size of 100 μm or less, and then cut into a size of 8.5 cm × 17.0 cm. The substrate was then acid-treated in 6N hydrochloric acid at room temperature for 10 minutes, washed with water, and dried. The dried conductive substrate was heated and sintered in a muffle furnace at 500°C for 10 minutes to form a nickel oxide layer on the surface of the conductive substrate. The weight of the conductive substrate after heating and sintering was measured using a PG503-S electronic balance manufactured by Mettler-Toledo K.K. Next, dinitrodiammine platinum nitric acid solution (Tanaka Kikinzoku, Pt concentration: 100 g / L), neodymium nitrate hexahydrate (Kanto Chemical, 3N5), and water were mixed so that the molar ratio of platinum element to neodymium element was 80:20, to prepare coating solution 2. A cathode 2 was produced under the same conditions as in Example 1-1, except that the cycle of the coating step, precursor layer forming step, and firing step was repeated 15 times using this coating liquid 2, and the weights of the catalyst and Pt were calculated.

[0125] (Examples 1-3) A bipolar element was produced under the same conditions as in Example 1-1, except that a cathode 3 produced as follows was used, and designated Example 1-3. -Cathode 3- The conductive substrate was a plain-woven mesh substrate made of nickel fine wires with a diameter of 0.15 mm woven at a mesh size of 40. The conductive substrate was blasted with alumina powder having a weight-average particle size of 100 μm or less, and then cut into a size of 8.5 cm × 17.0 cm. The substrate was then acid-treated in 6N hydrochloric acid at room temperature for 10 minutes, washed with water, and dried. The dried conductive substrate was heated and sintered in a muffle furnace at 500°C for 10 minutes to form a nickel oxide layer on the surface of the conductive substrate. The weight of the conductive substrate after heating and sintering was measured using a PG503-S electronic balance manufactured by Mettler-Toledo K.K. Next, dinitrodiammine platinum nitric acid solution (Tanaka Precious Metals, Pt concentration: 100 g / L), neodymium nitrate hexahydrate (Kanto Chemical, 3N5), and water were mixed so that the molar ratio of platinum to neodymium was 90:10, to prepare coating solution 3. A cathode 3 was produced under the same conditions as in Example 1-1, except that the cycle of the coating step, precursor layer forming step, and firing step was repeated 13 times using this coating liquid 3, and the weights of the catalyst and Pt were calculated.

[0126] (Examples 1-4) A bipolar element was produced under the same conditions as in Example 1-1, except that a cathode 4 produced as follows was used, and designated Example 1-4. -Cathode 4- The conductive substrate was a plain-woven mesh substrate made of nickel fine wires with a diameter of 0.15 mm woven at a mesh size of 40. The conductive substrate was blasted with alumina powder having a weight-average particle size of 100 μm or less, and then cut into a size of 8.5 cm × 17.0 cm. The substrate was then acid-treated in 6N hydrochloric acid at room temperature for 10 minutes, washed with water, and dried. The dried conductive substrate was heated and sintered in a muffle furnace at 500°C for 10 minutes to form a nickel oxide layer on the surface of the conductive substrate. The weight of the conductive substrate after heating and sintering was measured using a PG503-S electronic balance manufactured by Mettler-Toledo K.K. Next, dinitrodiammine Pt nitric acid solution (Tanaka Kikinzoku, Pt concentration: 100 g / L), Ni(II) nitrate hexahydrate (Kanto Chemical, 3N5), and water were mixed so that the molar ratio of Pt element to Ni element was 75:25, to prepare coating solution 4. A first catalyst layer was formed on the conductive substrate by repeating the cycle of the coating step and precursor layer formation step five times using this coating solution 4. The weight of this layer was measured using an electronic balance, and the difference from the weight of the conductive substrate before the first layer formation was divided by the area of ​​8.5 cm × 17.0 cm to calculate the weight of the first layer per unit area. The weight of the first layer was then calculated assuming that the weight of the first layer was the total weight of Pt and NiO contained in the first layer. Next, dinitrodiammine platinum nitric acid solution (Tanaka Kikinzoku, Pt concentration: 100 g / L), neodymium nitrate hexahydrate (Kanto Chemical, 3N5), and water were mixed so that the molar ratio of platinum element to neodymium element was 75:25, to prepare coating solution 5. Using this coating solution 5, a cycle of the coating step and the precursor layer forming step was repeated 11 times to form a second catalyst layer on the conductive substrate on which the first layer had been formed, and then post-baking was carried out in an air atmosphere at 500°C for 1 hour to produce a cathode 4. The weight of the cathode 4 was measured using an electronic balance, and the difference between the weight of the cathode 4 and the weight of the conductive substrate before the formation of the second layer was divided by the area of ​​8.5 cm×17.0 cm to calculate the weight of the second layer per unit area. The weight of the second layer was calculated assuming that the weight of the second layer was the total weight of Pt and Nd2O3 contained in the catalyst layer. The weight of the catalyst layer was calculated from the sum of the weight of the first layer and the weight of the second layer, and the weight of Pt contained in the catalyst layer was calculated from the sum of the weight of Pt contained in the first layer and the weight of Pt contained in the second layer.

[0127] (Examples 1-5) A bipolar element was produced under the same conditions as in Example 1-1, except that a cathode 5 produced as follows was used, and designated Example 1-5. -Cathode 5- The conductive substrate was a plain-woven mesh substrate made of nickel fine wires with a diameter of 0.15 mm woven at a mesh size of 40. The conductive substrate was blasted with alumina powder having a weight-average particle size of 100 μm or less, and then cut into a size of 8.5 cm × 17.0 cm. The substrate was then acid-treated in 6N hydrochloric acid at room temperature for 10 minutes, washed with water, and dried. The dried conductive substrate was heated and sintered in a muffle furnace at 500°C for 10 minutes to form a nickel oxide layer on the surface of the conductive substrate. The weight of the conductive substrate after heating and sintering was measured using a PG503-S electronic balance manufactured by Mettler-Toledo K.K. Next, dinitrodiammine platinum nitrate solution (Tanaka Precious Metals, Pt concentration: 100 g / L), neodymium nitrate hexahydrate (Kanto Chemical, 3N5), nickel (II) nitrate hexahydrate (Kanto Chemical, 3N5), and water were mixed so that the molar ratio of platinum, neodymium, and nickel was 75:17:8, to prepare coating solution 6. A cathode 5 was produced under the same conditions as in Example 1-1, except that the cycle of the coating step, precursor layer forming step, and firing step was repeated 17 times using this coating liquid 6. The weight was measured using an electronic balance, and the difference from the weight of the conductive base material before the catalyst layer was formed was divided by the area of ​​8.5 cm × 17.0 cm to calculate the weight of the catalyst layer per unit area. The weight of the catalyst layer was then calculated assuming that the weight of the catalyst layer was the total weight of PtO, Nd2O3, and NiO contained in the catalyst layer.

[0128] (Examples 1 to 6) A bipolar element was produced under the same conditions as in Example 1-1, except that a cathode 6 produced as follows was used, and designated Example 1-6. -Cathode 6- The conductive substrate was an electrolytic Ni foil with a gauge thickness of 16 μm. One side of this Ni foil was roughened by electrolytic Ni plating. The arithmetic mean roughness Ra of the roughened surface was 0.9 μm. This Ni foil was perforated by punching. The aperture ratio was 49%. This conductive substrate was cut into a piece of 8.5 cm x 17.0 cm, ultrasonically cleaned in isopropyl alcohol at room temperature for 10 minutes, and then dried. The dried conductive substrate was heated and sintered in a muffle furnace at 400°C for 10 minutes to form a nickel oxide layer on the surface of the conductive substrate. The weight of the conductive substrate after heating and sintering was measured using a PG503-S electronic balance manufactured by Mettler-Toledo K.K. The coating step used Coating Liquid 5. Coating Liquid 5 was sprayed onto the roughened side of the conductive substrate using a sprayer with 0.1 MPa compressed air as a carrier gas, and then the conductive substrate was dried at 60°C for 10 minutes to form a precursor layer. The conductive substrate on which the precursor layer had been formed was heated and baked in a muffle furnace at 400° C. for 10 minutes to pyrolyze the precursor layer. This cycle of the dip coating step, precursor layer forming step, and firing step was repeated 17 times, followed by post-firing at 400° C. for 1 hour in an air atmosphere to produce a cathode 6. The weight of this cathode 6 was measured using an electronic balance, and the difference between this weight and the weight of the conductive substrate before the formation of the catalyst layer was divided by the area of ​​8.5 cm×17.0 cm to calculate the weight of the catalyst layer per unit area. The weight of the catalyst layer was then calculated assuming that the weight of the catalyst layer was the total weight of PtO and Nd2O3 contained in the catalyst layer.

[0129] (Examples 1-7) A bipolar element was produced under the same conditions as in Example 1 except that a cathode 7 produced as follows was used, and designated Example 1-7. -Cathode 7- A cathode 7 was produced under the same conditions as in Example 1-1, except that the cycle of the coating step, precursor layer forming step, and firing step was repeated 10 times using Coating Liquid 1, and the weights of the catalyst and Pt were calculated.

[0130] (Examples 1-8) A bipolar element was produced under the same conditions as in Example 1-1, except that a cathode 8 produced as follows was used, and designated Example 1-8. -Cathode 8- A cathode 8 was produced under the same conditions as in Example 1-1, except that the cycle of the coating step, precursor layer forming step, and firing step was repeated 44 times using Coating Liquid 1, and the weights of the catalyst and Pt were calculated.

[0131] (Examples 1-9) A bipolar element was produced under the same conditions as in Example 1-1, except that a cathode 9 produced as follows was used, and designated Example 1-9. -Cathode 9- A cathode 9 was produced under the same conditions as in Example 1-1, except that the cycle of the coating step, precursor layer forming step, and firing step was repeated six times using Coating Liquid 1, and the weights of the catalyst and Pt were calculated.

[0132] (Examples 1-10) A bipolar element was produced under the same conditions as in Example 1-1, except that a cathode 10 produced as follows was used, and designated Example 1-10. -Cathode 10- A cathode 10 was produced under the same conditions as in Example 1, except that the cycle of the coating step, precursor layer forming step, and firing step was repeated 57 times using Coating Liquid 1, and the weights of the catalyst and Pt were calculated.

[0133] (Examples 1-11) A plain weave mesh made of 40-mesh woven nickel fine wires with a diameter of 0.15 mm was used as the anode 2, and a zero-gap type bipolar element was produced under the same conditions as in Example 1-1, except that the anode side used the same conductive elastic body, current collector, and rib as the cathode side. This was used to produce Example 1-11.

[0134] (Examples 1-12) A bipolar element was produced under the same conditions as in Example 1-1, and designated Example 1-12, except that an anode 3 was used, which was made of Ni expanded metal with a SW of 3.0 mm, a LW of 4.5 mm, a thickness of 0.75 mm, and an aperture ratio of 54% and was subjected to blasting treatment.

[0135] (Comparative Example 1-1) A bipolar element was prepared as Comparative Example 1-1 under the same conditions as in Example 1-1, except that a cathode 101 prepared as described below was used. -Cathode 101- A dinitrodiammine Pt nitric acid solution (Tanaka Kikinzoku K.K., Pt concentration: 100 g / L) and water were mixed to prepare coating liquid 7. Cathode 101 was produced under the same conditions as in Example 1-1, except that the cycle of the coating step, precursor layer forming step, and firing step was repeated 12 times using this coating liquid 7. The weight of the catalyst layer was then calculated assuming that the weight of the PtO contained in the catalyst layer was the weight of the Pt contained in the catalyst layer.

[0136] (Comparative Example 1-2) A bipolar element was produced as Comparative Example 1-2 under the same conditions as in Comparative Example 1-1, except that a cathode 102 produced as follows was used. -Cathode 102- Cathode 102 was produced under the same conditions as in Comparative Example 1-1, except that the cycle of the coating step, precursor layer formation step, and firing step was repeated 20 times using Coating Solution 7. The weight of the catalyst layer and the weight of Pt contained in the catalyst layer were calculated in the same manner as in Comparative Example 1-1.

[0137] (Comparative Examples 1-3) A bipolar element was prepared as Comparative Example 1-3 under the same conditions as in Example 1-1, except that a cathode 103 prepared as described below was used. -Cathode 103- Coating solution 8 was prepared by mixing dinitrodiammine platinum nitrate solution (Tanaka Precious Metals, Pt concentration: 100 g / L), Ce(III) nitrate hexahydrate (Kanto Chemical, special grade), and water so that the molar ratio of platinum to cerium was 50:50. A cathode 103 was produced under the same conditions as in Example 1-1, except that the cycle of the coating step, precursor layer forming step, and firing step was repeated 13 times using this coating liquid 8. The weight of the catalyst layer was then calculated assuming that the weight of the catalyst layer was the total weight of PtO and CeO contained in the catalyst layer.

[0138] (Comparative Examples 1-4) A bipolar element was produced as Comparative Example 1-4 under the same conditions as in Example 1-1, except that a cathode 104 produced as follows was used. -Cathode 104- A cathode 104 was produced in the same manner as in Example 1, except that the cycle of the coating step, the precursor layer forming step, and the firing step was repeated eight times using Coating Solution 8. The weight of the catalyst layer was then calculated assuming that the weight of the catalyst layer was the total weight of Pt and CeO contained in the catalyst layer.

[0139] (Comparative Examples 1-5) A bipolar element was produced as Comparative Example 1-5 under the same conditions as in Example 1-1, except that a cathode 105 produced as follows was used. -Cathode 105- Dinitrodiammine Pt nitric acid solution (Tanaka Kikinzoku, Pt concentration: 100 g / L), Ce(III) nitrate hexahydrate (Kanto Chemical, Kaga special grade), and water were mixed so that the molar ratio of Pt element to Ce element was 64:36, to prepare coating solution 9. A cathode 105 was produced under the same conditions as in Example 1-1, except that the cycle of the coating step, precursor layer forming step, and firing step was repeated 15 times using this coating liquid 9. The weight of the catalytic layer was then calculated assuming that the weight of the catalytic layer was the total weight of PtO and CeO contained in the catalytic layer.

[0140] The following tests (1) to (4) were carried out for each of the examples and comparative examples. The results are shown in Table 1. Test (1) Cathode discharge amount measurement method The discharge amount of the cathode was calculated by the three-electrode method as follows: The measurement device used was a potentiogalvanostat PARSTAT MC 1000 manufactured by Princeton Applied Research. The same cathode used in each example and comparative example was cut to 18 mm x 17 mm and fixed to a PTFE-coated nickel rod with a nickel screw. A Pt mesh was used as the counter electrode, and a silver-silver chloride (Ag / AgCl) glass electrode was used as the reference electrode. The electrolyte was a 34 wt% aqueous potassium hydroxide solution. The temperature of this electrolyte was adjusted to 70°C. First, a current density of -6 kA / m 2 After applying a reduction current of +15A / m for 1 hour, immediately after applying a reduction current of +15A / m without measuring the open circuit voltage. 2 An oxidation current of +15 A / m was applied. At this time, the cathode potential gradually increased from the hydrogen generation potential to a more noble potential. When the cathode potential reached +1.12 V (vs. RHE), the current was stopped. 2 The time from the start of current flow to the end of current flow and the absolute value of the current density of 15A / m 2 The cathode discharge rate (unit: C / m 2 ) was calculated.

[0141] Test (2) Measuring method for the electric double layer capacitance of the cathode The electric double layer capacitance of the cathode was calculated by the three-electrode method as follows. The measurement device used was a potentiogalvanostat PARSTAT MC 1000 manufactured by Princeton Applied Research. The same cathode used in each example and comparative example was cut to 18 mm x 17 mm and fixed to a PTFE-coated nickel rod with a nickel screw. A Pt mesh was used as the counter electrode, and a silver-silver chloride (Ag / AgCl) glass electrode was used as the reference electrode. The electrolyte was a 34 wt% aqueous potassium hydroxide solution. The temperature of this electrolyte was adjusted to 70°C. First, a current density of -6 kA / m 2 A reduction current of 0.47 V (vs. RHE) was applied for 1 hour. Then, cyclic voltammetry was performed with a potential sweep range of 0.40 V to 0.54 V (vs. RHE) at sweep rates of 50, 100, 200, and 400 mV / sec for 5 cycles each. Then, in the 5th cycle at each sweep rate, the average values ​​of the oxidation and reduction currents when the cathode potential was 0.47 V (vs. RHE) were plotted on the vertical axis and the sweep rate on the horizontal axis. The electric double layer capacity (unit: C / cm) was calculated from the slope of this plot. 2 ) was calculated.

[0142] Test (3) Anode discharge amount measurement method The discharge amount of the anode was calculated by the three-electrode method as follows: The measurement device used was a potentiogalvanostat PARSTAT MC 1000 manufactured by Princeton Applied Research. The same anode used in each example and comparative example was cut to 18 mm x 17 mm and fixed to a PTFE-coated nickel rod with a nickel screw. A Pt mesh was used as the counter electrode, and a silver-silver chloride (Ag / AgCl) glass electrode was used as the reference electrode. The electrolyte was a 34 wt% aqueous potassium hydroxide solution. The temperature of this electrolyte was adjusted to 70°C. First, a current density of +6 kA / m 2 After applying an oxidation current of -15A / m for 1 hour, the open circuit voltage was measured immediately. 2 A reduction current of -15 A / m was applied. At this time, the anode potential gradually decreased from the oxygen evolution potential to a less noble potential. When the anode potential reached +0.12 V (vs. RHE), the current was stopped. 2 The time from the start of current flow to the end of current flow and the absolute value of the current density of 15A / m 2The discharge rate of the anode is calculated from the product of 2 ) was calculated.

[0143] Test (4) Bipolar electrolytic cell power-off cycle test 1 For each of the Examples and Comparative Examples, a bipolar electrolytic cell was fabricated as follows, stacked in the order shown in Fig. 4. A bipolar electrolytic cell was constructed by stacking an anode terminal cell unit 51a using the anode described in each Example and Comparative Example, the diaphragm described above, a portion in which three sets of zero-gap bipolar elements of each Example and Comparative Example were stacked with the diaphragm described above sandwiched between them, the diaphragm described above, and a cathode terminal cell 51c using the cathode described in each Example and Comparative Example, in that order. Then, using this bipolar electrolytic cell, the electrolysis device shown in FIG. 3 was fabricated. The electrolysis device comprises a bipolar electrolytic cell 50, a liquid feed pump 71 for circulating the electrolyte, and a gas-liquid separation tank 72 for separating the electrolyte from hydrogen and / or oxygen. The gas-liquid separation tank 72 and the bipolar electrolytic cell 50 are filled with an electrolyte that is a 30% KOH aqueous solution. The liquid feed pump 71 circulates the electrolyte through the anode chamber 5a of the bipolar electrolytic cell 50, the gas-liquid separation tank 72 for the anode, and the anode chamber 5a, and also through the cathode chamber 5c of the bipolar electrolytic cell 50, the gas-liquid separation tank 72 for the cathode, and the cathode chamber 5c. The temperature was adjusted to 90°C. In the electrolysis device, the gas separated in the gas-liquid separation tank 72 is recovered through a pressure gauge 78, a pressure control valve 80, an oxygen concentration meter 75, or a hydrogen concentration meter 76. Electric power can be controlled by a rectifier 74. A flow meter 77 and a heat exchanger 79 are provided in the flow path of the circulating electrolyte. The arrows in Fig. 3 indicate the flow directions of the circulating liquid (electrolyte) and gas. The circulation flow path used SGP carbon steel piping with a Teflon (registered trademark) lining on the inner surface for the electrolyte contact part, and 20A piping was used. The gas-liquid separation tank 72 had a height of 1400 mm and a volume of 1 m 3 The following was used. The gas-liquid separation tank 72 is 1400 mm high and has a volume of 1 m 3 The following items were used. The liquid volume of each gas-liquid separation tank 72 was set to about 50% of the design volume. In the external header type electrolytic cell, the electrolysis frame, which serves as the housing for the bipolar element, is provided with four external pipes (anode inlet header 10ai, cathode inlet header 10ci, anode outlet header 10ao, and cathode outlet header 10co) for the circulation of the electrolyte. Each of these external pipes is connected to each electrode chamber of the electrolytic cell by an external hose. This piping structure is called the external header structure. The external header piping is divided into a cathode side external header piping and an anode side external header piping. Therefore, within each element, the electrolyte enters the cathode chamber 5c from the cathode inlet header 10ci via an external hose, and then flows from the cathode chamber 5c to the cathode outlet header 10co via an external hose. Similarly, on the anode side, the electrolyte enters the anode chamber 5a from the anode inlet header 10ai via an external hose, and then flows from the anode chamber 5a to the anode outlet header 10ao via an external hose. Because the inlet header of the external header is located below the electrolysis frame and the outlet header is located above the electrolysis frame, the electrolyte flows from bottom to top. It also rises in a direction approximately perpendicular to the electrode surface. A thermocouple is installed in the external hose of each cell, allowing the temperature difference before and after passing through the element to be measured. In this example, there are 29 anode chambers 5a and 29 cathode chambers 5c, and the structure is such that the electrolyte flows from the inlet header to the outlet header in each of the 29 chambers. In the cathode chamber 5c, hydrogen gas is generated by electrolysis, and in the anode chamber 5a, oxygen gas is generated, so that in the cathode outlet header 10co, a mixed-phase flow of electrolyte and hydrogen gas is formed, and in the anode outlet header 10ao, a mixed-phase flow of electrolyte and oxygen gas is formed. Electricity was applied from the rectifier 74 to the bipolar electrolytic cell 50 with respect to the areas of the cathode and anode under the conditions of Electrolysis Test 1 or Electrolysis Test 2 described below. The pressure inside the cell after the start of energization was measured with a pressure gauge 78, and was adjusted so that the cathode side pressure was 50 kPa and the oxygen side pressure was 49 kPa. The pressure was adjusted using a control valve 80 installed downstream of the pressure gauge 78. In the electrolysis device, the gas separated in the gas-liquid separation tank 72 is recovered through a pressure gauge 78, a pressure control valve 80, an oxygen concentration meter 75, or a hydrogen concentration meter 76. Electric power can be controlled by a rectifier 74. A flow meter 77 and a heat exchanger 79 are provided in the flow path of the circulating electrolyte. The electrolysis apparatus for alkaline water electrolysis was produced using a rectifier, an oxygen concentration meter, a hydrogen concentration meter, a pressure gauge, a liquid feed pump, a gas-liquid separation tank, a water supply device, and the like, all of which are commonly used in the relevant technical field.

[0144] When hydrogen generating electrolysis was performed using the above electrolysis apparatus, the potential of the zero-gap bipolar element was equal to the potential of the cathode, and the PTFE-coated Pt wire fixed near the cathode in the cathode chamber of the zero-gap bipolar element became an RHE electrode by coming into contact with hydrogen generated by electrolysis and was at a hydrogen generating potential; therefore, the potential difference between the zero-gap bipolar element and the PTFE-coated Pt wire was measured, and this potential difference was taken as the cathode overvoltage. Using the above electrolysis device, a current density of 6 kA / m 2 After 100 hours of continuous water electrolysis with positive current, the electrolysis was stopped for 5 minutes. 2 The test was performed with a 5-minute positive current application and a 5-minute stop. Each 5-minute positive current application and 5-minute stop was counted as one power-on / off cycle, and 1,500 power-on / off cycles were performed. The average cell voltage of the two cells not including the anode terminal cell unit 51a and the cathode terminal cell unit 51c during the first 5 minutes of positive current application after 100 hours of positive current application was defined as the initial cell voltage, the average cathode overvoltage of the two cells at this time was defined as the initial overvoltage, and the average cathode overvoltage of the two cells during the 1,500th power-on / off cycle was defined as the post-test overvoltage. [Table 1]

[0145] In test (4), the cathode overvoltage of each of Comparative Examples 1-1 to 1-5 increased by 60 mV or more after the test, whereas the increase in overvoltage of each of Examples 1-1 to 1-12 was suppressed to 30 mV or less, demonstrating significantly higher durability against 1,500 power interruptions. Furthermore, Examples 1-7 and 1-9 exhibited higher durability than Comparative Example 1-1 despite having a smaller catalyst weight and Pt weight than Comparative Example 1-1, and Examples 1-1 to 1-7, 1-9, 1-11, and 1-12 exhibited higher durability than Comparative Example 1-2 despite having a smaller catalyst weight and Pt weight than Comparative Example 1-2. These results demonstrate that a cathode having a catalyst layer containing Pt element in the molar ratio specified in the present invention and a lanthanoid element that is electrochemically stable as a trivalent ion within the potential window of water from pH 7 to pH 16 has high durability.

[0146] Furthermore, in Example 1-7, the overvoltage after the test decreased by 4 mV, whereas in Example 1-9, the overvoltage after the test increased by 21 mV. It is believed that durability decreases if the weight of the catalyst layer is too low. Also, it is believed that if the discharge amount is too small, the potential of the cathode becomes too noble when the current is stopped, causing more severe deterioration. From these results, it is believed that the weight of the catalyst layer is 4.5 g / m 2 The Pt weight is preferably 3.5 g / m or more. 2 More than 1500C / m is preferable. 2 The above was found to be preferable. Furthermore, Example 1-8 had an initial overvoltage of 111 mV and an overvoltage after the test of 120 mV, while Example 1-10 had an initial overvoltage of 119 mV and an overvoltage after the test of 130 mV. While both had high durability, they maintained a higher overvoltage than the other Examples. Since the oxides or hydroxides of lanthanoid elements contained in the catalyst layer are insulators or conductors with higher electrical resistance than metals, it is believed that if the catalyst weight is too high, the electrical resistance will increase. From this result, the weight of the catalyst layer is 20 g / m 2 Hereafter, the weight of Pt is 15g / m 2 The following has been found to be preferable:

[0147] Furthermore, there is a positive correlation between the discharge amount of the cathode and the electric double layer capacity, and the electric double layer capacity is 0.01 F / cm 2 ~0.15F / cm 2 was found to be preferable.

[0148] Next, Examples 2-1 to 2-21 and Comparative Examples 2-1 to 2-6 will be described.

[0149] Example 2-1 As in Example 1-1, a cathode 1 and an anode 1 were used.

[0150] (Example 2-2) As in Example 1-2, a cathode 2 and an anode 1 were used.

[0151] (Example 2-3) As in Example 1-3, a cathode 3 and an anode 1 were used.

[0152] (Examples 2-4) As in Example 1-4, a cathode 4 and an anode 1 were used.

[0153] (Examples 2-5) As in Examples 1-5, a cathode 5 and an anode 1 were used.

[0154] (Examples 2-6) As in Examples 1-6, a cathode 6 and an anode 1 were used.

[0155] (Examples 2-7) As in Examples 1-7, a cathode 7 and an anode 1 were used.

[0156] (Examples 2-8) As in Examples 1-8, a cathode 8 and an anode 1 were used.

[0157] (Examples 2-9) As in Examples 1-9, a cathode 9 and an anode 1 were used.

[0158] (Examples 2-10) As in Examples 1-10, a cathode 10 and an anode 1 were used.

[0159] (Example 2-11) As in Example 1-11, a cathode 1 and an anode 2 were used.

[0160] (Example 2-12) As in Example 1-12, a cathode 1 and an anode 3 were used.

[0161] (Example 2-13) The cathode 11 and the anode 1 prepared as follows were used. -Cathode 11- The conductive substrate was a plain-woven mesh substrate made of nickel fine wires with a diameter of 0.15 mm woven at a mesh size of 40. The conductive substrate was blasted with alumina powder having a weight-average particle size of 100 μm or less, and then cut into a size of 8.5 cm × 17.0 cm. The substrate was then acid-treated in 6N hydrochloric acid at room temperature for 10 minutes, washed with water, and dried. The dried conductive substrate was heated and sintered in a muffle furnace at 500°C for 10 minutes to form a nickel oxide layer on the surface of the conductive substrate. The weight of the conductive substrate after heating and sintering was measured using a PG503-S electronic balance manufactured by Mettler-Toledo K.K. Next, dinitrodiammine platinum nitric acid solution (Tanaka Kikinzoku, Pt concentration: 100 g / L), neodymium nitrate hexahydrate (Kanto Chemical, 3N5), and water were mixed so that the molar ratio of platinum to neodymium was 65:35, to prepare coating solution 10. A cathode 11 was produced under the same conditions as in Example 1-1, except that the cycle of the coating step, precursor layer forming step, and firing step was repeated 19 times using this coating liquid 10, and the weights of the catalyst and Pt were calculated.

[0162] (Example 2-14) The cathode 12 and the anode 1 prepared as follows were used. -Cathode 12- The conductive substrate was a plain-woven mesh substrate made of nickel fine wires with a diameter of 0.15 mm woven at a mesh size of 40. The conductive substrate was blasted with alumina powder having a weight-average particle size of 100 μm or less, and then cut into a size of 8.5 cm × 17.0 cm. The substrate was then acid-treated in 6N hydrochloric acid at room temperature for 10 minutes, washed with water, and dried. The dried conductive substrate was heated and sintered in a muffle furnace at 500°C for 10 minutes to form a nickel oxide layer on the surface of the conductive substrate. The weight of the conductive substrate after heating and sintering was measured using a PG503-S electronic balance manufactured by Mettler-Toledo K.K. Next, dinitrodiammine platinum nitric acid solution (Tanaka Kikinzoku, Pt concentration: 100 g / L), neodymium nitrate hexahydrate (Kanto Chemical, 3N5), and water were mixed so that the molar ratio of platinum element to neodymium element was 95:5, to prepare coating solution 11. A cathode 12 was produced under the same conditions as in Example 1-1, except that the cycle of the coating step, precursor layer forming step, and firing step was repeated 17 times using this coating liquid 11, and the weights of the catalyst and Pt were calculated.

[0163] (Example 2-15) The cathode 13 and the anode 1 prepared as follows were used. -Cathode 13- The conductive substrate was a plain-woven mesh substrate made of nickel fine wires with a diameter of 0.15 mm woven at a mesh size of 40. The conductive substrate was blasted with alumina powder having a weight-average particle size of 100 μm or less, and then cut into a size of 8.5 cm × 17.0 cm. The substrate was then acid-treated in 6N hydrochloric acid at room temperature for 10 minutes, washed with water, and dried. The dried conductive substrate was heated and sintered in a muffle furnace at 500°C for 10 minutes to form a nickel oxide layer on the surface of the conductive substrate. The weight of the conductive substrate after heating and sintering was measured using a PG503-S electronic balance manufactured by Mettler-Toledo K.K. Next, a dinitrodiammine platinum nitric acid solution (Tanaka Kikinzoku, Pt concentration: 100 g / L), Sm nitrate hexahydrate (Kanto Chemical, 3N5), and water were mixed so that the molar ratio of platinum to sm was 75:25, to prepare coating solution 11. A cathode 13 was produced under the same conditions as in Example 1-1, except that the cycle of the coating step, precursor layer forming step, and firing step was repeated 17 times using this coating liquid 11. The weight of the catalytic layer was then calculated assuming that the weight of the catalytic layer was the total weight of PtO and SmO contained in the catalytic layer.

[0164] (Example 2-16) The cathode 14 and the anode 1 prepared as follows were used. -Cathode 14- The conductive substrate was a plain-woven mesh substrate made of nickel fine wires with a diameter of 0.15 mm woven at a mesh size of 40. The conductive substrate was blasted with alumina powder having a weight-average particle size of 100 μm or less, and then cut into a size of 8.5 cm × 17.0 cm. The substrate was then acid-treated in 6N hydrochloric acid at room temperature for 10 minutes, washed with water, and dried. The dried conductive substrate was heated and sintered in a muffle furnace at 500°C for 10 minutes to form a nickel oxide layer on the surface of the conductive substrate. The weight of the conductive substrate after heating and sintering was measured using a PG503-S electronic balance manufactured by Mettler-Toledo K.K. Next, dinitrodiammine Pt nitric acid solution (Tanaka Kikinzoku, Pt concentration: 100 g / L), Gd nitrate hexahydrate (Kanto Chemical, 3N5), and water were mixed so that the molar ratio of Pt element to Gd element was 75:25 to prepare coating liquid 12. A cathode 14 was produced under the same conditions as in Example 1-1, except that the cycle of the coating step, precursor layer forming step, and firing step was repeated 17 times using this coating liquid 12. The weight of the catalytic layer was then calculated assuming that the weight of the catalytic layer was the total weight of PtO and GdO contained in the catalytic layer.

[0165] (Example 2-17) The cathode 15 and the anode 1 prepared as follows were used. -Cathode 15- The conductive substrate was a plain-woven mesh substrate made of nickel fine wires with a diameter of 0.15 mm woven at a mesh size of 40. The conductive substrate was blasted with alumina powder having a weight-average particle size of 100 μm or less, and then cut into a size of 8.5 cm × 17.0 cm. The substrate was then acid-treated in 6N hydrochloric acid at room temperature for 10 minutes, washed with water, and dried. The dried conductive substrate was heated and sintered in a muffle furnace at 500°C for 10 minutes to form a nickel oxide layer on the surface of the conductive substrate. The weight of the conductive substrate after heating and sintering was measured using a PG503-S electronic balance manufactured by Mettler-Toledo K.K. Next, dinitrodiammine Pt nitric acid solution (Tanaka Kikinzoku, Pt concentration: 100 g / L), Tb nitrate hexahydrate (Kanto Chemical, 3N5), and water were mixed so that the molar ratio of Pt element to Tb element was 75:25, to prepare coating liquid 13. A cathode 15 was produced under the same conditions as in Example 1-1, except that the cycle of the coating step, precursor layer forming step, and firing step was repeated 17 times using this coating liquid 13. The weight of the catalytic layer was then calculated assuming that the weight of the catalytic layer was the total weight of PtO and TbO contained in the catalytic layer.

[0166] (Example 2-18) The cathode 16 and the anode 1 prepared as follows were used. -Cathode 16- The conductive substrate was a plain-woven mesh substrate made of nickel fine wires with a diameter of 0.15 mm woven at a mesh size of 40. The conductive substrate was blasted with alumina powder having a weight-average particle size of 100 μm or less, and then cut into a size of 8.5 cm × 17.0 cm. The substrate was then acid-treated in 6N hydrochloric acid at room temperature for 10 minutes, washed with water, and dried. The dried conductive substrate was heated and sintered in a muffle furnace at 500°C for 10 minutes to form a nickel oxide layer on the surface of the conductive substrate. The weight of the conductive substrate after heating and sintering was measured using a PG503-S electronic balance manufactured by Mettler-Toledo K.K. Next, dinitrodiammine Pt nitric acid solution (Tanaka Kikinzoku, Pt concentration: 100 g / L), Dy nitrate pentahydrate (Kanto Chemical, 3N5), and water were mixed so that the molar ratio of Pt element to Dy element was 75:25, to prepare coating liquid 14. A cathode 16 was produced under the same conditions as in Example 1-1, except that the cycle of the coating step, precursor layer forming step, and firing step was repeated 17 times using this coating liquid 14. The weight of the catalyst layer was then calculated assuming that the weight of the catalyst layer was the total weight of PtO and DyO contained in the catalyst layer.

[0167] (Example 2-19) The cathode 17 and the anode 1 prepared as follows were used. -Cathode 17- The conductive substrate was a plain-woven mesh substrate made of nickel fine wires with a diameter of 0.15 mm woven at a mesh size of 40. The conductive substrate was blasted with alumina powder having a weight-average particle size of 100 μm or less, and then cut into a size of 8.5 cm × 17.0 cm. The substrate was then acid-treated in 6N hydrochloric acid at room temperature for 10 minutes, washed with water, and dried. The dried conductive substrate was heated and sintered in a muffle furnace at 500°C for 10 minutes to form a nickel oxide layer on the surface of the conductive substrate. The weight of the conductive substrate after heating and sintering was measured using a PG503-S electronic balance manufactured by Mettler-Toledo K.K. Next, a first layer of the catalyst layer was formed on the conductive substrate by repeating the cycle of the coating step and the precursor layer forming step four times using Coating Liquid 3. The weight was measured using an electronic balance, and the difference from the weight of the conductive substrate before the first layer was formed was divided by the area of ​​8.5 cm × 17.0 cm to calculate the weight of the first layer per unit area. The weight of the first layer was calculated assuming that the weight of the first layer was the total weight of Pt and Nd2O3 contained in the first layer. Subsequently, a cycle of the coating step and the precursor layer forming step was repeated 10 times using the coating liquid 1 to form a second catalyst layer on the conductive substrate on which the first layer had been formed, followed by post-baking at 500°C for 1 hour in an air atmosphere to produce a cathode 17. The weight of the cathode 17 was measured using an electronic balance, and the difference between the weight of the cathode 17 and the weight of the conductive substrate before the formation of the second layer was divided by the area of ​​8.5 cm×17.0 cm to calculate the weight of the second layer per unit area. The weight of the second layer was calculated assuming that the weight of the second layer was the total weight of Pt and Nd2O3 contained in the catalyst layer. The weight of the catalyst layer was calculated from the sum of the weight of the first layer and the weight of the second layer, and the weight of Pt contained in the catalyst layer was calculated from the sum of the weight of Pt contained in the first layer and the weight of Pt contained in the second layer.

[0168] (Example 2-20) The cathode 18 and the anode 1 prepared as follows were used. -Cathode 18- The conductive substrate was an electrolytic Ni foil with a gauge thickness of 16 μm. One side of this Ni foil was roughened by electrolytic Ni plating. The arithmetic mean roughness Ra of the roughened surface was 0.6 μm. This Ni foil was perforated by punching. The aperture ratio was 49%. This conductive substrate was cut into a piece of 8.5 cm x 17.0 cm, ultrasonically cleaned in isopropyl alcohol at room temperature for 10 minutes, and then dried. The dried conductive substrate was heated and sintered in a muffle furnace at 400°C for 10 minutes to form a nickel oxide layer on the surface of the conductive substrate. The weight of the conductive substrate after heating and sintering was measured using a PG503-S electronic balance manufactured by Mettler-Toledo K.K. The coating step used Coating Liquid 5. Coating Liquid 5 was sprayed onto the roughened side of the conductive substrate using a sprayer with 0.1 MPa compressed air as a carrier gas, and then the conductive substrate was dried at 60°C for 10 minutes to form a precursor layer. The conductive substrate on which the precursor layer had been formed was heated and baked in a muffle furnace at 400° C. for 10 minutes to pyrolyze the precursor layer. This cycle of the dip coating step, precursor layer forming step, and firing step was repeated 17 times, followed by post-firing at 400° C. for 1 hour in an air atmosphere to produce a cathode 6. The weight of this cathode 18 was measured using an electronic balance, and the difference between this weight and the weight of the conductive substrate before the catalyst layer was formed was divided by the area of ​​8.5 cm×17.0 cm to calculate the weight of the catalyst layer per unit area. The weight of the catalyst layer was then calculated assuming that the weight of the catalyst layer was the total weight of PtO and Nd2O3 contained in the catalyst layer.

[0169] Example 2-21 The cathode 19 and the anode 1 prepared as follows were used. -Cathode 18- The conductive substrate was a plain-woven mesh substrate made of nickel fine wires with a diameter of 0.15 mm woven at a mesh size of 40. The conductive substrate was blasted with alumina powder having a weight-average particle size of 100 μm or less, and then cut into a size of 8.5 cm × 17.0 cm. The substrate was then acid-treated in 6N hydrochloric acid at room temperature for 10 minutes, washed with water, and dried. The dried conductive substrate was heated and sintered in a muffle furnace at 500°C for 10 minutes to form a nickel oxide layer on the surface of the conductive substrate. The weight of the conductive substrate after heating and sintering was measured using a PG503-S electronic balance manufactured by Mettler-Toledo K.K. Next, dinitrodiammine platinum nitrate solution (Tanaka Precious Metals, Pt concentration: 100 g / L), neodymium nitrate hexahydrate (Kanto Chemical, 3N5), palladium nitrate solution (Tanaka Precious Metals, Pd concentration: 100 g / L), and water were mixed so that the molar ratio of platinum, neodymium, and nickel was 75:17:8, to prepare coating solution 6. A cathode 5 was produced under the same conditions as in Example 1-1, except that the cycle of the coating step, precursor layer forming step, and firing step was repeated 17 times using this coating liquid 6. The weight was measured using an electronic balance, and the difference from the weight of the conductive base material before the catalyst layer was formed was divided by the area of ​​8.5 cm × 17.0 cm to calculate the weight of the catalyst layer per unit area. The weight of the catalyst layer was then calculated assuming that the weight of the catalyst layer was the total weight of PtO, Nd2O3, and PdO contained in the catalyst layer.

[0170] (Comparative Example 2-1) As in Comparative Example 1-1, a cathode 101 and an anode 1 were used.

[0171] (Comparative Example 2-2) As in Comparative Example 1-2, the cathode 102 and the anode 1 were used.

[0172] (Comparative Example 2-3) As in Comparative Example 1-3, the cathode 103 and the anode 1 were used.

[0173] (Comparative Example 2-4) As in Comparative Example 1-4, the cathode 104 and the anode 1 were used.

[0174] (Comparative Example 2-5) As in Comparative Example 1-5, the cathode 105 and the anode 1 were used.

[0175] (Comparative Example 2-6) The cathode 106 prepared as follows was used. -Cathode 106- The conductive substrate was a plain-woven mesh substrate made of nickel fine wires with a diameter of 0.15 mm woven at a mesh size of 40. The conductive substrate was blasted with alumina powder having a weight-average particle size of 100 μm or less, and then cut into a size of 8.5 cm × 17.0 cm. The substrate was then acid-treated in 6N hydrochloric acid at room temperature for 10 minutes, washed with water, and dried. The dried conductive substrate was heated and sintered in a muffle furnace at 500°C for 10 minutes to form a nickel oxide layer on the surface of the conductive substrate. The weight of the conductive substrate after heating and sintering was measured using a PG503-S electronic balance manufactured by Mettler-Toledo K.K. Next, dinitrodiammine platinum nitric acid solution (Tanaka Kikinzoku, Pt concentration: 100 g / L), neodymium nitrate hexahydrate (Kanto Chemical, 3N5), and water were mixed so that the molar ratio of platinum element to neodymium element was 45:55, to prepare coating solution 15. A cathode 106 was produced under the same conditions as in Example 1-1, except that the cycle of the coating step, precursor layer forming step, and firing step was repeated 26 times using this coating liquid 15, and the weight of the catalyst, Pt, was calculated.

[0176] The above-mentioned tests (1) to (3) and the following test (5) were carried out for each of the examples and comparative examples. The results are shown in Table 2.

[0177] Test (5) Reverse current cycle test 1 simulating a 200-pair bipolar electrolytic cell A reverse current cycle test was carried out by the three-electrode method using a potentiogalvanostat PARSTAT MC 1000 manufactured by Princeton Applied Research, simulating a 200-pair bipolar electrolytic cell as follows. First, in a 200-pair bipolar electrolytic cell, the average value of the reverse current flowing through each cell after electrolysis was stopped was calculated to be 15 A / m2 using an equivalent circuit calculation. Subsequently, discharge curves at the above current densities were obtained for the cathode and anode described in each example and comparative example. The cathode was cut to an 18mm x 17mm size and fixed to a PTFE-coated nickel rod with nickel screws. A platinum mesh was used as the counter electrode, and a silver-silver chloride (Ag / AgCl) glass electrode was used as the reference electrode. The electrolyte was a 34 wt% aqueous potassium hydroxide solution. The temperature of the electrolyte was adjusted to 70°C. A reductive current of -6 kA / m² was applied for 1 hour, followed immediately by an oxidative current of +15 A / m² without any intervening open-circuit voltage measurements. The cathode potential gradually increased from the hydrogen generation potential to a more noble potential. The current was stopped when the cathode potential reached +1.12 V (vs. RHE). The absolute value of the cumulative charge, calculated as the product of the current density and the current duration, was plotted on the horizontal axis, and the cathode potential on the vertical axis, to obtain the cathode discharge curve. Next, the anode was cut to an 18mm x 17mm size and fixed to a PTFE-coated nickel rod with nickel screws. A platinum mesh was used as the counter electrode, and a silver-silver chloride (Ag / AgCl) glass electrode was used as the reference electrode. The electrolyte was a 34 wt% aqueous potassium hydroxide solution. The temperature of the electrolyte was adjusted to 70°C. An oxidizing current of +6 kA / m² was applied for 1 hour, followed immediately by a reducing current of -15 A / m² without any intervening open-circuit voltage measurements. The anode potential gradually decreased from the oxygen evolution potential to a more noble potential. The current was stopped when the anode potential reached +0.12 V (vs. RHE). The absolute value of the accumulated charge, calculated as the product of the current density and the current duration, was plotted on the horizontal axis, and the anode potential on the vertical axis, to obtain the anode discharge curve. The discharge curve of the cathode and the discharge curve of the anode were then superimposed, and the potential at which they intersected was set as the potential reached by the reverse current when the current flow was stopped. An example is shown in Figure 7. Using the reverse current density obtained as above and the ultimate potential of the reverse current in each example and each comparative example as conditions, a reverse current cycle test was carried out as follows. The cathode was cut to an 18mm x 17mm size and fixed to a PTFE-coated nickel rod with a nickel screw. A platinum mesh was used as the counter electrode, and a silver-silver chloride (Ag / AgCl) glass electrode was used as the reference electrode. The electrolyte was a 34 wt% potassium hydroxide aqueous solution. The temperature of this electrolyte was adjusted to 70°C. Under these conditions, the overvoltage was measured at a current density of -6 kA / m². Ohmic losses, which could not be completely eliminated even with the three-electrode method, were measured using the AC impedance method, and the overvoltage was corrected based on the measured ohmic losses. Next, as a pretreatment for the cathode, a reduction current with a current density of -6 kA / m² was applied for 5 hours, followed immediately by an oxidation current of +15 A / m² without any intervening open-circuit voltage measurements. During this time, the cathode potential gradually increased from the hydrogen generation potential to a more noble potential. When the cathode potential reached the reverse current potential for each example, a reduction current of -6 kA / m² was immediately applied for 1 minute without any intervening open-circuit voltage measurements. This combination of an oxidation current and a 1-minute reduction current constituted one reverse current cycle, and the reverse current cycle was applied 10,000 times. After this, the overvoltage at a current density of -6 kA / m² was measured again, and this was taken as the overvoltage after the reverse current cycle test. [Table 2]

[0178] In test (5), the cathode overvoltage of each of Comparative Examples 2-1 to 2-5 increased by 50 mV or more after the test, whereas the increase in overvoltage of each of Examples 2-1 to 2-21 was kept to 30 mV or less, demonstrating significantly higher durability against 10,000 reverse current cycles. In addition, in Comparative Example 2-6, no electrolysis current was generated, and no hydrogen bubbles were observed due to electrolysis. This is thought to be because the oxides or hydroxides of lanthanoid elements present in the catalytic layer are insulators or conductors with higher electrical resistance than metals, and therefore if the ratio of lanthanoid elements to Pt is too high, the electronic conductivity in the catalytic layer becomes significantly high. Furthermore, the initial overvoltage in Example 2-13 is higher than in Examples 2-1 to 2-12 and 2-14 to 2-21. This is thought to be because, for the same reason as above, the high ratio of lanthanoid elements to Pt reduces the electronic conductivity of the catalytic layer. These results demonstrate that a cathode having a catalytic layer containing Pt element and a lanthanoid element that is electrochemically stable as a trivalent ion within the potential window of water from pH 7 to pH 16 in the molar ratio specified in the present invention can maintain high energy conversion efficiency over a long period of time even in 200 pairs of alkaline water electrolysis cells including 199 bipolar electrolytic cells.

[0179] Comparing Examples 2-1 to 2-12 with Comparative Examples 2-1 to 2-5, the results in Test (5) were generally similar to those in Examples 1-1 to 1-12 and Comparative Examples 1-1 to 1-5 in Test (4). The reason why the overvoltage increase after 1,500 power interruptions in Comparative Examples 1 to 5 in Test (4) was greater than the overvoltage increase after 10,000 reverse current cycles in Comparative Examples 2-1 to 2-5 in Test (5), despite the smaller number of cycles, is thought to be that in Test (4), the interruption time during which reverse current occurred was 5 minutes, while in Test (5), the reverse current application time was extremely short, on the order of several tens of seconds, and therefore the cathode damage per cycle was smaller in Test (5).

[0180] Comparing Example 2-4 and Example 2-19, Example 2-4 had a smaller overvoltage rise in Test (5). This is thought to be because the cathode 4 of Example 2-4 contains the same Ni element as the conductive substrate in the first layer of the catalytic layer, improving the affinity between the catalytic layer and the conductive substrate and suppressing peeling and falling of the catalytic layer and the substrate due to reverse current.

[0181] The overvoltage of Example 2-21 after 10,000 reverse current cycles was significantly lower than that of Examples 2-1 to 2-20. The cathodes after these tests were embedded in epoxy resin and then processed using an Ar ion beam (BIB) to prepare cross sections of the cathodes. The BIB-processed cross sections were observed using an SEM (Hitachi High-Technologies Corporation S-4800) to obtain backscattered electron images (magnifications: 3,000x, 10,000x, and 30,000x). This cross-sectional observation revealed that the NiO layer between the Ni substrate and the catalytic layer in Example 2-21 was significantly thinner than in Examples 2-1 to 2-20. This is thought to be because Pd has the hydrogen molecular dissociation and hydrogen absorption capabilities to dissociate hydrogen molecules generated by electrolysis into atomic hydrogen and store it in the catalytic layer. The reducing power of this atomic hydrogen suppresses the growth of the NiO layer due to oxidation of the Ni substrate during reverse current. Since the NiO layer is an insulator or a conductor with higher electrical resistance than metals, it is thought that this growth suppression contributed to the suppression of the rise in overvoltage.

[0182] Next, Examples 3-1 and 3-2 and Comparative Examples 3-1 to 3-3 will be described.

[0183] Example 3-1 A bipolar element was produced under the same conditions as in Example 1-1, except that a cathode 20 and an anode 4 produced as described below were used, and designated Example 3-1. -Cathode 20- A cathode 20 was produced under the same conditions as in Example 1-1, except that the cycle of the coating step, precursor layer forming step, and firing step was repeated 17 times using Coating Liquid 4, and the weights of the catalyst and Pt were calculated.

[0184] -Anode 4- A suspension was prepared by mixing and stirring 100 parts by mass of nickel oxide powder with a particle size of 0.2 to 2 μm, 2.25 parts by mass of gum arabic, 0.7 parts by mass of carboxymethyl cellulose, 0.001 parts by mass of sodium lauryl sulfate, and 100 parts by mass of water. Granules with a particle size of 5 to 50 μm were prepared from the suspension by spray drying using a spray dryer granulator.

[0185] A Ni porous substrate was prepared using Ni expanded metal with a SW of 3.0 mm, LW of 4.5 mm, thickness of 1.2 mm, and an aperture ratio of 54%. It was then subjected to a blasting process. The granulated material was sprayed onto the Ni porous substrate using a plasma spraying method, with a spray rate of 0.5 kg / m² on each side, for a total of 1.0 kg / m² per projected area (excluding the pores) of the Ni porous substrate. A 1:0.8 mixture of argon and nitrogen was used as the plasma gas in the plasma spraying process. This electrode was placed in a quartz tube. The quartz tube was inserted into a tubular furnace, the quartz tube was heated to 200°C, and a hydrogen stream was continuously supplied into the quartz tube to reduce the catalytic layer. The Ni porous substrate with the Ni catalytic layer formed thereon, prepared by the above process, was designated anode 4.

[0186] (Example 3-2) A bipolar element was produced under the same conditions as in Example 3-1 except that the cathode 4 was used, and designated as Example 3-2.

[0187] (Comparative Example 3-1) A bipolar element was produced under the same conditions as in Example 3-1 except that the cathode 101 was used, and designated as Comparative Example 3-1.

[0188] (Comparative Example 3-2) A bipolar element was produced as Comparative Example 3-2 under the same conditions as in Example 1-1, except that a cathode 107 and an anode 4 produced as described below were used. -Cathode 107- Dinitrodiammine Pt nitric acid solution (Tanaka Precious Metals, Pt concentration: 100 g / L), Ce(III) nitrate hexahydrate (Kanto Chemical, special grade), and water were mixed so that the molar ratio of Pt element to Ce element was 75:25, to prepare coating solution 16. A cathode 107 was produced under the same conditions as in Example 1-1, except that the cycle of the coating step, precursor layer forming step, and firing step was repeated 17 times using this coating liquid 16. The weight of the catalytic layer was then calculated assuming that the weight of the catalytic layer was the total weight of PtO and CeO contained in the catalytic layer.

[0189] (Comparative Example 3-3) A bipolar element was fabricated as Comparative Example 3-3 under the same conditions as in Example 1-1, except that a cathode 108 and an anode 4 fabricated as described below were used. -Cathode 108- Cathode 108 was produced under the same conditions as in Example 1-4, except that a first layer of the catalytic layer was formed on the conductive base material by repeating a cycle of the coating step and the precursor layer forming step five times using Coating Liquid 4, the weight of the first layer was considered to be the total weight of Pt and NiO contained in the first layer, and the weight of Pt contained in the first layer was calculated; a second layer of the catalytic layer was formed on the conductive base material on which the first layer had been formed by repeating a cycle of the coating step and the precursor layer forming step 11 times using Coating Liquid 16, and the weight of the second layer was considered to be the total weight of Pt and CeO2 contained in the catalytic layer, and the weight of Pt contained in the second layer was calculated.

[0190] For each example and comparative example, the above-mentioned tests (1) to (3) and the following tests (6) and (7) were carried out. The results are shown in Table 3.

[0191] Test (6) Calculation of [IPt / (IPt+IPtO)] X-ray diffraction measurements were performed using a Rigaku Corporation SmartLab fully automated multipurpose X-ray diffractometer. The sample was mounted on a silicon anti-reflection plate to avoid background from the sample plate. To minimize X-ray spillover from the sample, the sample size was at least 2 cm square, and the center of the sample was aligned with the center of the X-ray beam. The sample height was then adjusted and measurements were performed. Measurements were performed using a Cu target as a rotating anode and CuKα radiation. The X-ray output was 45 kV and 200 mA. The optical configuration was a reflective parallel optical system with a multilayer mirror on the entrance side. The entrance optical elements were a 2.5° Soller slit, a 10 mm-wide vertical divergence slit, and a 1 mm-wide divergence slit. The receiving optical elements were a 0.5° parallel slit analyzer (PSA) and a hybrid multidimensional pixel detector, HyPix-3000. The measurement was performed using the θ / 2θ method, in which scanning was performed so that the angle between the sample surface and the X-ray source and the angle between the sample surface and the detector were constant, and the diffraction angle defined by 2θ was scanned in the range of 10 to 90 degrees. The angle step was 0.05 degrees, and the scanning speed was 2 degrees / minute, and an X-ray diffraction chart of the cathode in each example was obtained. The resulting X-ray diffraction chart was subjected to peak separation using the graph processing software "Igor Pro." Peak separation was performed over the angle range 2θ = 25° to 2θ = 42°. After subtracting the background of the straight line connecting the measurement points at both ends of the angle, three Gaussian distribution functions with medians at (1) 30.0-36.0°, (2) 36.5-38.0°, and (3) 38.0-42.0° were assumed. Peak separation was performed using the peak intensity, peak median, and full width at half maximum as parameters. Each peak represents a combination of CuKα1 and CuKα2 contributions, but these were treated as a single peak without separation. The three Gaussian distribution functions correspond to the reflections of (1) the (200) and (111) planes of PtO, (2) the (111) plane of NiO, and (3) the (111) plane of Pt metal, respectively. After peak separation, the area of ​​each peak was calculated, and the peak area of ​​(3) was designated as IPt, and the peak area of ​​(1) was designated as IPtO, and [IPt / (IPt+IPtO)] was calculated.

[0192] Test (7) Bipolar electrolytic cell power-off cycle test 2 For each of the Examples and Comparative Examples, a bipolar electrolytic cell was fabricated as follows, stacked in the order shown in Fig. 4. A bipolar electrolytic cell was constructed by stacking an anode terminal cell unit 51a using the anode described in each Example and Comparative Example, the diaphragm described above, a portion in which three sets of zero-gap bipolar elements of each Example and Comparative Example were stacked with the diaphragm described above sandwiched between them, the diaphragm described above, and a cathode terminal cell 51c using the cathode described in each Example and Comparative Example, in that order. Then, using this bipolar electrolytic cell, the electrolysis device shown in FIG. 3 was fabricated. The electrolysis device comprises a bipolar electrolytic cell 50, a liquid feed pump 71 for circulating the electrolyte, and a gas-liquid separation tank 72 for separating the electrolyte from hydrogen and / or oxygen. The gas-liquid separation tank 72 and the bipolar electrolytic cell 50 are filled with an electrolyte that is a 30% KOH aqueous solution. The liquid feed pump 71 circulates the electrolyte through the anode chamber 5a of the bipolar electrolytic cell 50, the gas-liquid separation tank 72 for the anode, and the anode chamber 5a, and also through the cathode chamber 5c of the bipolar electrolytic cell 50, the gas-liquid separation tank 72 for the cathode, and the cathode chamber 5c. The temperature was adjusted to 90°C. In the electrolysis device, the gas separated in the gas-liquid separation tank 72 is recovered through a pressure gauge 78, a pressure control valve 80, an oxygen concentration meter 75, or a hydrogen concentration meter 76. Electric power can be controlled by a rectifier 74. A flow meter 77 and a heat exchanger 79 are provided in the flow path of the circulating electrolyte. The arrows in Fig. 3 indicate the flow directions of the circulating liquid (electrolyte) and gas. The circulation flow path used SGP carbon steel piping with a Teflon (registered trademark) lining on the inner surface for the electrolyte contact part, and 20A piping was used. The gas-liquid separation tank 72 had a height of 1400 mm and a volume of 1 m 3 The following was used. The gas-liquid separation tank 72 is 1400 mm high and has a volume of 1 m 3 The following items were used. The liquid volume of each gas-liquid separation tank 72 was set to about 50% of the design volume. In the external header type electrolytic cell, the electrolysis frame, which serves as the housing for the bipolar element, is provided with four external pipes (anode inlet header 10ai, cathode inlet header 10ci, anode outlet header 10ao, and cathode outlet header 10co) for the circulation of the electrolyte. Each of these external pipes is connected to each electrode chamber of the electrolytic cell by an external hose. This piping structure is called the external header structure. The external header piping is divided into a cathode side external header piping and an anode side external header piping. Therefore, within each element, the electrolyte enters the cathode chamber 5c from the cathode inlet header 10ci via an external hose, and then flows from the cathode chamber 5c to the cathode outlet header 10co via an external hose. Similarly, on the anode side, the electrolyte enters the anode chamber 5a from the anode inlet header 10ai via an external hose, and then flows from the anode chamber 5a to the anode outlet header 10ao via an external hose. Because the inlet header of the external header is located below the electrolysis frame and the outlet header is located above the electrolysis frame, the electrolyte flows from bottom to top. It also rises in a direction approximately perpendicular to the electrode surface. A thermocouple is installed in the external hose of each cell, allowing the temperature difference before and after passing through the element to be measured. In this example, there are 29 anode chambers 5a and 29 cathode chambers 5c, and the structure is such that the electrolyte flows from the inlet header to the outlet header in each of the 29 chambers. In the cathode chamber 5c, hydrogen gas is generated by electrolysis, and in the anode chamber 5a, oxygen gas is generated, so that in the cathode outlet header 10co, a mixed-phase flow of electrolyte and hydrogen gas is formed, and in the anode outlet header 10ao, a mixed-phase flow of electrolyte and oxygen gas is formed. Electricity was applied from the rectifier 74 to the bipolar electrolytic cell 50 with respect to the areas of the cathode and anode under the conditions of Electrolysis Test 1 or Electrolysis Test 2 described below. The pressure inside the cell after the start of energization was measured with a pressure gauge 78, and was adjusted so that the cathode side pressure was 50 kPa and the oxygen side pressure was 49 kPa. The pressure was adjusted using a control valve 80 installed downstream of the pressure gauge 78. In the electrolysis device, the gas separated in the gas-liquid separation tank 72 is recovered through a pressure gauge 78, a pressure control valve 80, an oxygen concentration meter 75, or a hydrogen concentration meter 76. Electric power can be controlled by a rectifier 74. A flow meter 77 and a heat exchanger 79 are provided in the flow path of the circulating electrolyte. The electrolysis apparatus for alkaline water electrolysis was produced using a rectifier, an oxygen concentration meter, a hydrogen concentration meter, a pressure gauge, a liquid feed pump, a gas-liquid separation tank, a water supply device, and the like, all of which are commonly used in the relevant technical field.

[0193] When hydrogen generating electrolysis was performed using the above electrolysis apparatus, the potential of the zero-gap bipolar element was equal to the potential of the cathode, and the PTFE-coated Pt wire fixed near the cathode in the cathode chamber of the zero-gap bipolar element became an RHE electrode by coming into contact with hydrogen generated by electrolysis and was at a hydrogen generating potential; therefore, the potential difference between the zero-gap bipolar element and the PTFE-coated Pt wire was measured, and this potential difference was taken as the cathode overvoltage. Using the above electrolysis device, a current density of 6 kA / m 2 After 100 hours of continuous water electrolysis with positive current, the electrolysis was stopped for 5 minutes. 2 The test was performed with a 5-minute positive current application and a 5-minute stop. Each 5-minute positive current application and 5-minute stop was counted as one power-on / off cycle, and 500 power-on / off cycles were performed. The average cell voltage of the two cells excluding the anode terminal cell unit 51a and the cathode terminal cell unit 51c during the first 5 minutes of positive current application after 100 hours of positive current application was defined as the initial cell voltage, the average cathode overvoltage of the two cells at this time was defined as the initial overvoltage, and the average cathode overvoltage of the two cells during the 500th power-on / off cycle was defined as the post-test overvoltage.

[0194] [Table 3]

[0195] In test (7), the cathode overvoltage of each of Comparative Examples 3-1 to 3-3 increased by 150 mV or more after the test, whereas the increase in overvoltage of each of Examples 3-1 to 3-3 was kept to 40 mV or less, demonstrating significantly higher durability against 500 power interruptions. These results demonstrate that a cathode having a catalyst layer containing Pt element in the molar ratio specified in the present invention and a lanthanoid element that is electrochemically stable as a trivalent ion within the potential window of water from pH 7 to pH 16 has high durability.

[0196] A comparison of Example 3-1 and Comparative Example 3-2 reveals that the durability against power interruption differs significantly depending on whether the catalytic layer contains Nd or Ce. This is thought to be because Nd is electrochemically stable as a trivalent ion within the potential window of water from pH 7 to pH 16, whereas Ce undergoes oxidation-reduction reactions from trivalent to tetravalent and from tetravalent to trivalent within the potential window of water from pH 7 to pH 16. Figure 8 shows the results of cyclic voltammetry of cathode 20 measured at a potential sweep rate of 100 mV / sec in 8 M KOH at 70 °C, and Figure 9 shows the results of cyclic voltammetry of cathode 105 measured under similar conditions. Figure 9 shows a pair of oxidation peaks near +0.77 V vs. RHE and reduction peaks near +0.56 V vs. RHE, indicating a redox reaction not present in Figure 8. Referring to Atlas of Electrochemical Equilibria in Aqueous Solutions (by Marcel Pourbaix, published by the National Association of Corrosion Engineers, 1974), this redox reaction is thought to be a redox reaction between Ce3+ and Ce4+. Therefore, we used X-ray photoelectron spectroscopy to analyze the chemical state of Nd in cathode 20, which was subjected to a positive current of 6 kA / m² for 5 hours in a three-electrode cell, and the chemical state of Ce in cathode 105, which was subjected to a positive current of 6 kA / m² for 5 hours. The electrodes were cut into pieces approximately 3 mm x 20 mm and placed in a recess holder provided with the instrument. A molybdenum mask with a 5 mm hole diameter was placed over the electrode and secured in place with a dedicated leaf spring and screws, grounding the sample. X-ray photoelectron spectroscopy measurements were performed using an ULVAC-PHI VersaProbe II. The excitation source was monochromated Al Kα at 15 kV x 3.3 mA, the analysis area was approximately 200 μm diameter, the pass energy was 23.5 eV (narrow scan), the energy step was 0.1 eV, and no charge compensation was performed. Figure 10 shows the analysis results for cathode 20, and Figure 11 shows the analysis results for cathode 105. The cathode 20 remained unchanged both before and after the current was applied, with Nd remaining in trivalent ion form. However, the Ce in the cathode 105 contained a mixture of trivalent and tetravalent ions before the current was applied, but after the current was applied, the tetravalent ions became the main constituent, indicating that a change in valence occurred during the current application. Furthermore, the surfaces of cathode 20 and cathode 105 after test (7) were observed under SEM. Significant loss of the catalyst layer was confirmed in cathode 105. Furthermore, it was confirmed that the areas where the catalyst layer barely remained were cracked into flakes. Figure 12 shows the surface of the catalyst layer of cathode 20 after test (7) (magnification 3000x). Figure 12 also shows the surface of the barely remaining catalyst layer of cathode 105 after test (7) (magnification 3000x). From the above, it is thought that Ce undergoes oxidation-reduction reactions from trivalent to tetravalent and from tetravalent to trivalent within the potential window of water from pH 7 to pH 16, which causes changes in the crystal morphology within the catalyst layer, leading to the catalyst layer collapsing and peeling off from the substrate, resulting in low durability during power-off cycles.In contrast, Nd is electrochemically stable as a trivalent ion within the potential window of water from pH 7 to pH 16, and therefore exhibits high reverse current durability.

[0197] Comparing Examples 3-1 and 3-2, Example 3-2 exhibited a more suppressed increase in overvoltage after the power-off cycle test. This is believed to be due to the fact that the proportion of Pt present as metal in the catalytic layer of cathode 4 of Example 3-2 and its crystallinity were higher than those of cathode 20 of Example 3-1. Figure 14 shows the XRD measurement results for cathode 20 and cathode 4. As shown by the comparison of [IPt / (IPt+IPtO)], the Pt in the catalytic layer of cathode 20 of Example 3-1 was mainly amorphous PtO, whereas the Pt in cathode 4 of Example 3-2 was mainly crystalline Pt. PtO in the cathode catalytic layer was reduced to Pt metal crystals by electrolytic reduction during positive current application. However, by crystallizing the Pt metal prior to electrolysis, the adhesion between the Pt crystalline particles in the catalytic layer was improved, which is believed to be why attrition of the catalytic layer was suppressed. Although the mechanism is unclear, the inventors have confirmed that forming a catalyst layer containing Pt and Ni as the first layer and a catalyst layer containing Pt and a lanthanoid element as the second layer promotes the growth of Pt metal crystals more than simply forming a catalyst layer containing Pt and a lanthanoid element. These results show that when the peak area of ​​X-rays diffracted by the (111) plane of the Pt metal in the catalyst layer is IPt, and the peak area of ​​X-rays diffracted by the (200) and (111) planes of PtO is IPtO, it is more preferable for the value of [IPt / (IPt+IPtO)] to be 0.1 or greater. However, as shown in Comparative Example 3-1, even if the X-ray diffraction peak satisfies the above conditions, this effect cannot be obtained unless the present invention is used, in which the catalyst layer contains a lanthanoid element that is electrochemically stable as a trivalent ion within the potential window of water from pH 7 to pH 16.

[0198] Furthermore, compared with Examples 1-1 to 1-12, Examples 3-1 and 3-2 had lower initial cell voltages. This was due to the effect of the anode, which is due to the fact that anodes 1 to 3 in Examples 1-1 to 1-12 did not have a catalyst layer, whereas anode 4 in Examples 3-1 and 3-2 had a catalyst layer. Generally, forming a catalyst layer on an anode increases the amount of reverse current discharge, and the reverse current associated with power interruption sweeps the cathode potential more noble, resulting in greater degradation due to reverse current. Therefore, cell voltage and durability generally have a trade-off relationship. From this perspective, the significance of the present invention, which achieves high power interruption durability even when a bipolar element is formed with an anode having a catalyst layer formed thereon, is significant in order to further increase the energy efficiency of hydrogen production by electrolysis.

[0199] Next, Examples 4-1 to 4-4 and Comparative Examples 4-1 to 4-3 will be described. (Example 4-1) As in Example 3-1, a cathode 20 and an anode 4 were used.

[0200] (Example 4-2) As in Example 3-2, a cathode 4 and an anode 4 were used.

[0201] (Example 4-2) As in Example 3-2, a cathode 4 and an anode 4 were used.

[0202] (Example 4-3) The cathode 21 and the anode 4 prepared as follows were used. -Cathode 21- Cathode 21 was produced under the same conditions as in Example 1-4, except that a first layer of the catalytic layer was formed on the conductive base material by repeating a cycle of the coating step and the precursor layer forming step twice using Coating Liquid 4, the weight of the first layer was considered to be the total weight of Pt and NiO contained in the first layer, and the weight of Pt contained in the first layer was calculated; and a second layer of the catalytic layer was formed on the conductive base material on which the first layer had been formed by repeating a cycle of the coating step and the precursor layer forming step 14 times using Coating Liquid 5, and the weight of the second layer was considered to be the total weight of Pt and NdO contained in the catalytic layer, and the weight of Pt contained in the second layer was calculated.

[0203] (Example 4-4) The cathode 22 and the anode 4 were prepared as follows. -Cathode 21- Cathode 22 was produced under the same conditions as in Example 1-4, except that a first layer of the catalytic layer was formed on the conductive base material by repeating a cycle of the coating step and the precursor layer forming step eight times using Coating Liquid 4, and the weight of the first layer was calculated assuming that the weight of the first layer was the total weight of Pt and NiO contained in the first layer, and a second layer of the catalytic layer was formed on the conductive base material on which the first layer had been formed by repeating a cycle of the coating step and the precursor layer forming step nine times using Coating Liquid 5, and the weight of the second layer was calculated assuming that the weight of the second layer was the total weight of Pt and NdO contained in the catalytic layer.

[0204] (Comparative Example 4-1) As in Comparative Example 3-1, a cathode 104 and an anode 4 were used.

[0205] (Comparative Example 4-2) As in Comparative Example 3-2, the cathode 105 and the anode 4 were used.

[0206] (Comparative Example 4-3) As in Comparative Example 3-3, the cathode 106 and the anode 4 were used.

[0207] For each example and comparative example, the above-mentioned tests (1) to (3) and (6) and the following test (8) were carried out. The results are shown in Table 4.

[0208] Test (8) Reverse current cycle test 2 simulating a 200-pair bipolar electrolytic cell A reverse current cycle test was carried out by the three-electrode method using a potentiogalvanostat PARSTAT MC 1000 manufactured by Princeton Applied Research, simulating a 200-pair bipolar electrolytic cell as follows. First, in a 200-pair bipolar electrolytic cell, the average value of the reverse current flowing through each cell after electrolysis was stopped was calculated to be 15 A / m2 using an equivalent circuit calculation. Subsequently, discharge curves at the above current densities were obtained for the cathode and anode described in each example and comparative example. The cathode was cut to an 18mm x 17mm size and fixed to a PTFE-coated nickel rod with nickel screws. A platinum mesh was used as the counter electrode, and a silver-silver chloride (Ag / AgCl) glass electrode was used as the reference electrode. The electrolyte was a 34 wt% aqueous potassium hydroxide solution. The temperature of the electrolyte was adjusted to 70°C. A reductive current of -6 kA / m² was applied for 1 hour, followed immediately by an oxidative current of +15 A / m² without any intervening open-circuit voltage measurements. The cathode potential gradually increased from the hydrogen generation potential to a more noble potential. The current was stopped when the cathode potential reached +1.25 V (vs. RHE). The absolute value of the cumulative charge, calculated as the product of the current density and the duration of the current application, was plotted on the horizontal axis, and the cathode potential on the vertical axis to obtain the cathode discharge curve. Next, the anode was cut to an 18mm x 17mm size and fixed to a PTFE-coated nickel rod with nickel screws. A platinum mesh was used as the counter electrode, and a silver-silver chloride (Ag / AgCl) glass electrode was used as the reference electrode. The electrolyte was a 34 wt% aqueous potassium hydroxide solution. The temperature of the electrolyte was adjusted to 70°C. An oxidizing current of +6 kA / m² was applied for 1 hour, followed immediately by a reducing current of -15 A / m² without any intervening open-circuit voltage measurements. The anode potential gradually decreased from the oxygen evolution potential to a more noble potential. The current was stopped when the anode potential reached +0.12 V (vs. RHE). The absolute value of the accumulated charge, calculated as the product of the current density and the current duration, was plotted on the horizontal axis, and the anode potential on the vertical axis, to obtain the anode discharge curve. The discharge curve of the cathode and the discharge curve of the anode were then superimposed, and the potential at which they intersected was set as the potential reached by the reverse current when the current flow was stopped. An example is shown in Figure 15. Using the reverse current density obtained as above and the ultimate potential of the reverse current in each example and each comparative example as conditions, a reverse current cycle test was carried out as follows. The cathode was cut to an 18mm x 17mm size and fixed to a PTFE-coated nickel rod with a nickel screw. A platinum mesh was used as the counter electrode, and a silver-silver chloride (Ag / AgCl) glass electrode was used as the reference electrode. The electrolyte was a 34 wt% potassium hydroxide aqueous solution. The temperature of this electrolyte was adjusted to 70°C. Under these conditions, the overvoltage at a current density of -6 kA / m2 was measured. Ohmic losses that could not be completely eliminated even with the three-electrode method were measured using the AC impedance method, and the overvoltage was corrected based on the measured ohmic losses. Next, as a pretreatment for the cathode, a reduction current at a current density of -6 kA / m2 was applied for 5 hours, followed immediately by an oxidation current of +15 A / m2 without any intervening open-circuit voltage measurements. During this time, the cathode potential gradually increased from the hydrogen generation potential to a more noble potential. When the cathode potential reached the reverse current potential for each example, a reduction current of -6 kA / m2 was immediately applied for 1 minute without any intervening open-circuit voltage measurements. This combination of an oxidation current and a 1-minute reduction current constituted one reverse current cycle, and the reverse current cycle was applied 2,000 times. After this, the overvoltage at a current density of -6 kA / m2 was measured again, and this was defined as the overvoltage after the reverse current cycle test. [Table 4]

[0209] Comparing Examples 4-1 and 4-2 with Comparative Examples 4-1 to 4-3, the results in Test (8) were generally similar to those in Examples 3-1 and 3-2 and Comparative Examples 3-1 to 3-3 in Test (7). These results and Examples 4-3 and 4-4 demonstrated that a cathode having a catalytic layer containing Pt element and a lanthanoid element that is electrochemically stable as a trivalent ion within the potential window of water from pH 7 to pH 16, in a molar ratio specified by the present invention, can maintain high energy conversion efficiency over a long period of time even in 200 pairs of alkaline water electrolysis electrolytic cells including 199 bipolar electrolytic cells for alkaline water electrolysis. Furthermore, it was found that, where IPt is the peak area of ​​X-rays diffracted by the (111) plane of Pt metal in the catalytic layer, and IPtO is the peak area of ​​X-rays diffracted by the (200) and (111) planes of PtO, the value of [IPt / (IPt+IPtO)] is preferably 0.1 or greater. [Industrial Applicability]

[0210] According to the present invention, it is possible to provide a cathode for hydrogen generation that maintains high energy conversion efficiency for a long period of time without an increase in overvoltage even when hydrogen generation is repeatedly started and stopped. [Explanation of symbols]

[0211] 1 Bulkhead 2 electrodes 2a anode 2c cathode 2e Elastic body 2r current collector 3 Outer frame 4 Diaphragm 5 Electrode chamber 5a Anode chamber 5c cathode chamber 5i Electrolyte inlet 5o Electrolyte outlet 6. Ribs 7 Gasket 8 PFA coated Pt wire 9a nozzle 9b Cap nut 9c PTFE board 9d EPDM board 10. Header 10o External Header 10ai Anode Inlet Header 10ao Anode Outlet Header 10ci cathode inlet header 10co cathode outlet header 50 bipolar electrolyzer 51g fast head, loose head 51i Insulating plate 51a Anode terminal element 51c Cathode Terminal Element 51r tie rod 60 Multi-pole element 65 Electrolysis Cell 70 Electrolyzer 71 Liquid transfer pump 72 Gas-liquid separation tank 74 Rectifier 75 Oxygen concentration meter 76 Hydrogen concentration meter 77 Flow meter 78 Pressure Gauge 79 Heat exchanger 80 Pressure control valve Z Zero gap structure

Claims

1. At least one of Pt, Pt oxide, and Pt hydroxide on a surface of a conductive substrate; At least one of a metal, an oxide, and a hydroxide of a lanthanoid element that is electrochemically stable as a trivalent ion within the potential window of water of pH 7 or more and pH 16 or less; A cathode for hydrogen generation having a catalyst layer containing A cathode for generating hydrogen, characterized in that the molar ratio of Pt element to lanthanoid element (Pt:lanthanoid) in the catalyst layer is 95:5 to 65:

35.

2. 2. The electrode according to claim 1, which is a cathode for alkaline water electrolysis.

3. 3. The cathode according to claim 1, wherein the catalyst layer contains the same type of element as that contained in the conductive substrate.

4. 3. The cathode according to claim 1, wherein the catalytic layer comprises a first layer formed on the surface of the conductive substrate and a second layer formed on the first layer, the first layer having different molar ratios of Pt and lanthanoid.

5. 5. The cathode according to claim 4, wherein the molar ratio of the lanthanoid element in the second layer is greater than the molar ratio of the lanthanoid element in the first layer.

6. 5. The cathode according to claim 4, wherein the first layer contains the same type of element as that contained in the conductive substrate.

7. 3. The cathode according to claim 1, wherein a value of [IPt / (IPt+IPtO)] is 0.1 or more, where IPt is a peak area of ​​X-rays diffracted by a (111) plane of Pt metal in the catalytic layer, and IPtO is a peak area of ​​X-rays diffracted by a (200) plane and a (111) plane of PtO.

8. 3. The cathode according to claim 1, wherein the lanthanoid element is at least one of Nd, Sm, Gd, Tb, and Dy.

9. 9. The cathode according to claim 8, wherein the lanthanoid element is Nd.

10. 3. The cathode according to claim 1, wherein the conductive substrate contains Ni.

11. 11. The cathode according to claim 10, wherein the conductive substrate is a plain weave mesh made by weaving fine Ni wires having a wire diameter of 0.05 mm to 1.00 mm with a mesh size of 20 to 60.

12. The cathode according to claim 10, wherein the conductive substrate is a Ni foil having a thickness of 100 μm or less.

13. 4. The cathode according to claim 3, wherein the catalyst layer contains Pt, Nd, and Ni.

14. 5. The cathode according to claim 4, wherein the catalyst layer comprises the first layer containing Pt and Ni and the second layer containing Pt and Nd.

15. The amount of the catalyst layer carried is 4.5 g / m ２ 20g / m or more ２ 3. The cathode according to claim 1, wherein:

16. The amount of Pt element carried in the catalyst layer is 3.5 g / m ２ 15g / m or more ２ 3. The cathode according to claim 1, wherein:

17. 3. The cathode according to claim 1, wherein the catalyst layer contains a hydrogen storage alloy.

18. 18. The cathode according to claim 17, wherein the catalyst layer contains Pd.

19. 6 kA / m ２ After applying a reduction current of 15 A / m for 1 hour ２ The cumulative discharge amount until the potential reaches +1.12 V (vs. RHE) is 1500 C / m ２ More than 10000C / m ２ 3. The cathode according to claim 1, wherein:

20. The electric double layer capacity is 0.01 F / cm ２ 0.15F / cm or more ２ 3. The cathode according to claim 1, wherein:

21. a coating step of coating the conductive substrate with a coating liquid containing at least a Pt compound and a lanthanoid compound; a precursor layer forming step of drying the coating liquid to form a precursor layer containing Pt and a lanthanoid on the conductive substrate; a calcination step of heating the precursor layer at a temperature in the range of 300°C to 800°C to obtain a catalyst layer; 3. The method for producing a cathode according to claim 1, further comprising the steps of repeating the steps in order two or more times.

22. a first coating step of coating the conductive substrate with a first coating liquid containing at least a Pt compound and a lanthanoid compound; a first precursor layer forming step of drying the first coating liquid to form a first precursor layer containing Pt and a lanthanoid on the conductive substrate; a first firing step of heating the first precursor layer at a temperature in the range of 300°C to 800°C to obtain the first layer; After the first step, which is repeated two or more times in sequence, a second coating step of coating a second coating liquid containing at least a Pt compound and a lanthanoid compound in a molar ratio different from that of the first layer on the conductive substrate on which the first layer has been formed; a second precursor layer forming step of drying the second coating liquid to form a second precursor layer on the first layer, the second precursor layer containing Pt and a lanthanoid in a molar ratio different from that of the first layer; a second firing step in which the second precursor layer is heated at a temperature in the range of 300°C to 800°C to obtain a second layer; The method for producing a cathode according to claim 4, further comprising repeating the second step two or more times in sequence.

23. a first coating step of coating the conductive substrate containing Ni with a first coating liquid containing at least a Pt compound and Ni; a first precursor layer forming step of drying the first coating liquid to form a first precursor layer containing Pt and Ni on the conductive base material; a first firing step of heating the first precursor layer at a temperature in the range of 300°C to 800°C to obtain the first layer; After the first step, which is repeated two or more times in sequence, a second coating step of coating a second coating liquid containing at least a Pt compound and an Nd compound onto the conductive substrate on which the first layer has been formed; a second precursor layer forming step of drying the second coating liquid to form a second precursor layer containing Pt and Nd on the first coating layer; a second firing step in which the second precursor layer is heated at a temperature in the range of 300°C to 800°C to obtain a second layer; The method for producing a cathode according to claim 14, further comprising repeating the second step two or more times in sequence.

24. A bipolar electrolytic cell comprising the cathode according to claim 1 or 2.

25. The cathode and the anode are provided, 6 kA / m ２ After applying an oxidation current of 15 A / m for 1 hour ２ The cumulative discharge amount until the potential reaches +0.12 V (vs. RHE) is 6 kA / m ２ After applying a reduction current of 15 A / m for 1 hour ２ 25. The bipolar electrolytic cell according to claim 24, wherein the cumulative discharge amount is greater than the cumulative discharge amount until the potential reaches +1.12 V (vs. RHE) when an oxidation current of 1.0 V is passed through the bipolar electrolytic cell.

26. 6 kA / m ２ After applying an oxidation current of 15 A / m for 1 hour ２ The cumulative discharge amount until the potential reaches +0.12 V (vs. RHE) is 10,000 C / m ２ More than 300000C / m ２ 26. The bipolar electrolytic cell of claim 25, wherein:

27. ​​A cathode and an anode, 25. The bipolar electrolytic cell of claim 24, wherein the anode comprises Ni.

28. 3 to 200 bipolar electrolytic cells according to claim 24; at least one cathode terminal cell; at least one anode terminal cell; An electrolytic cell for alkaline water electrolysis, comprising:

29. A method for producing hydrogen, comprising electrolyzing alkali-containing water using the alkaline water electrolysis cell according to claim 28 to produce hydrogen.

30. 30. The method for producing hydrogen according to claim 29, wherein water containing alkali is electrolyzed using a variable power supply that involves repeating positive current application and interruption of positive current application to produce hydrogen.

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